Yes, Jews still step on a glass object (not necessarily a drinking glass - I think I've heard of lightbulbs being used - something that will break and go "crunch") at their weddings. I think you might be confused on its meaning, though. If you would allow me to explain...
The breaking of the glass does not "symbolize the performance of the union". Rather, it is l'zecher hachurban, that is, it is done in remembrance of the destruction of the Temple. We are reminded at our time of greatest joy not to forget. Lest we be tempted to think that our lives are complete, and that the world is in its ideal state. As the Psalmist wrote:
"If I forget thee, O Jerusalem, let my right hand wither, let my tongue cleave to my palate if I do not remember you, if I do not set Jerusalem above my highest joy."
So the breaking of the glass is a way of setting Jerusalem above our highest joy. In fact, at a few weddings I've been to, the guy singing music for the wedding ceremony itself, would sing this exact verse (in its original language, of course) the moment before the chossan (groom) steps on the glass. After this moment of reflection, however, we resume with the celebration, everyone shouting their congratulations: "Mazel tov!" So, the mazel tov isn't tied to the breaking of the glass per se (which is really supposed to be somber remembrance), but rather to the wedding ceremony which is ended with the breaking of said glass.
So yes, we still do, but it's not for the reason that you thought. Now, would we be offended if you, a non-Jewish woman, chose to incorporate this remembrance into your wedding ceremony? Well, the bottom line is, you can do whatever the heck you want. The real question is: Why? I have to be honest - it sounds kind of weird to me. And if you have any Jewish guests at your wedding, they might be confused. The remembrance of the Temple is kind of a Jewish thing, and there's really no way it would have the same meaning to a non-Jew. And please don't misconstrue this for an insult - it's simply fact. A gentile isn't going to find meaning in the remembrance of the Jewish Temple the same way a Hindu isn't going to find profound significance in the remembrance of Jesus' crucifixion. It's just not relevant. Now, there may be some non-Jews who mourn for the Temple, perhaps the B'nei Noach (this is a religious sect of non-Jews who share the same beliefs of Jews, but choose not to convert but rather keep the Seven Noachide Laws, those commandments that the Hebrew Bible lays out for non-Israelites), because when the Temple stood, sacrifices WERE offered on behalf of the non-Jewish nations as well. In fact, the Talmud states that if the Romans had realized how much they benefited from the Temple, they would never have destroyed it.
Sorry, got a little off topic there. I'm curious as to whether or not your groom is Jewish. Because I have to tell you, if you're not Jewish, and your husband-to-be isn't Jewish, then breaking a glass at the ceremony is just kind of weird. But if you're not Jewish, and your husband is Jewish, then breaking a glass as part of the ceremony would indeed be offensive to observant Jews. I'll leave you with a story from my own experience that actually fits your question quite well...
I was once dating a girl who convinced me to come with her to her sister's wedding. Now, the girl I was dating was Jewish, as was her sister, but the groom was not. Now, Jewish Law (as found in the Bible and expounded upon in our Oral Tradition) actually prohibits Jews from marrying non-Jews. The reasons for this would be too difficult to explain here, so I'll simplify it by saying that Judaism encourages people to remain Jewish, and to marry Jewish, so as to raise Jewish families. Those who intermarry, even if their children retain some sense of Jewish identity (the children of a Jewish woman are considered Jewish according to Torah Law regardless of who the father is, the children of a Jewish man and a non-Jewish woman however, are not), it's pretty much guaranteed that within two or three generations, Jewish identity will be lost. Suffice it to say for the sake of this answer that everything I'm telling you is supported by the statistics. Okay, so why does it matter that Judaism teaches that Jews should marry Jewish, and that intermarrying is a surefire way for a Jew to end the chain of Jewish continuity as it would otherwise pertain to their descendants? Well, this wedding I went to was a hokey interfaith ceremony. For example, members of each family walked to the center of the room, holding candles, and using those candles to light a larger "unity candle" in the middle of the room. You know, ceremonies that are designed to look ancient or something, but with no actual tradition behind them. Frankly, I find this kind of thing insulting both to the bride's Judaism and the groom's Catholicism. But that's not what we're talking about here - we were talking about the breaking of the glass. Well, this wedding I went to borrowed that ceremony as well. Here's the thing:
A Jewish woman marrying a non-Jewish man means that she's likely to sever what little connection to Judaism she had in the first place. Even if not, their children (who are Jewish by definition) are likely to grow up never knowing Judaism, and are themselves likely to intermarry. Ultimately, their children aren't going to be Jewish, and what would have been a new branch of the family tree of Israel has, in effect, been cut off before it could even grow! What may have been destined to be a significant part of the Jewish people is preemptively destroyed. Then, as we make this destruction official, the non-Jewish groom steps on a glass. Suddenly, the symbolism is changed. No longer are we remembering the destruction of the Temple and in so doing expressing the sincere wish to see it rebuilt. Rather, we are CONTINUING the destruction of the Temple. This young man, who of course couldn't possibly have known better (clearly the bride didn't know, and if the Jewish spouse isn't acquainted with these essential Jewish ideas, how could we expect the non-Jew to be?), performs a deed that, to him probably "symbolized the performance of the union." In fact, in this case, it is a travesty, and at least from the Jewish perspective, and affront to G-d. He's not remembering the destruction of the Temple - he's perpetuating it! Pardon my language here, but I think it's important to make this point as clearly as possible: It's like, the Temple was burned to the ground, and two thousand years later, this guy is basically pissing on the ashes.
How, if at all, does this apply to you? Well, I hate to say it, but you have a right to know: If your husband-to-be is Jewish, and he's stepping on a glass as he marries you, then the symbolism is basically the same (though perhaps not as deliciously ironic as a gentile doing it) as the story described above. If neither of you are Jewish, on the other hand, it's just weird. It sounds like you're trying to find a tradition to draw from, and in so doing, don't really understand or care about the symbolic significance. Still, if that's what floats your boat, go for it. My advice to you would be to look into your own family history, look into your own traditions, and find something meaningful. And if you REALLY look hard, and can't find anything that holds meaning for you, then start your own tradition. Taking a Jewish tradition and divorcing it from its meaning is just silly. I personally wouldn't be offended, but I'd think it weird, and a little sad that you couldn't create a ceremony on the basis of your own cultural traditions, which probably have a lot of history and meaning to them. Maybe you haven't given them a fair chance, or maybe you simply haven't looked. Be proud of who you are!
And of course, if you convert to Judaism in accordance with Torah Law, and your husband ends up being Jewish, well, then ignore everything I've said and do the glass thing. :) Of course, if you wound up being Jewish, you'd know that there's a lot more neato symbolism to a Jewish wedding ceremony than the one part that everyone knows about from watching movies like Fiddler.
Sorry if it rained on your parade, but I hope this answered your question, and if you have any further questions, feel free to contact me directly.