I think a year is ideal.
However, some of us have to go beyond that. I'm getting married tomorrow and our engagement has been 2.5 years long! This is why it happened:
~Got engaged at the end of December 2007.
~ Decided upon a spring wedding and of course spring of 2008 was going to be way too soon. There was no way to pull that off
~ We set a date for June 2009
~ Sat down to do our fiances and realized that in order to be able to have our friends and closest family members there, we would need to save more. We felt it would be stupid of us to put it all on credit cards and go into debt.
~Changed the date to June 5th 2010
We're not doing anything extravagant, but we live in a very expensive area. Also, we're paying a mortgage in said expensive area so it took a bit to save. We have less than 75 guests, cut corners everywhere, did A LOT of do-it-yourself stuff, and it still costs a lot.
Pros to the long engagement: All the money was saved, plenty of time to plan
Cons: The waiting felt like forever. We've been ready to get married for so long and it kinda sucked to wait.