I got engaged exacly 18 months before our wedding date. When I started calling venues shortly afterward, several said, "I'm glad you called, because we have had a lot of people interested in May 2013!" (Several others said to call back closer to May because they didn't do anything >1 year in advance.)
Now that I'm looking at caterers, the first place I called said, "I'm actually surprised to see that May 25th 2013 is still open! Let's book a tasting ASAP."
ARE YOU KIDDING ME, DUDE?! This is over 16 months before the wedding!! Don't try to tell me you're already booking up May 2013. This is a relatively small-ish town (Chapel Hill, NC)!
Do you girls hear this kind of thing a lot? I have a hard time believing it.... yet it still makes me want to act fast (arrrghh!!)