FI and I are getting married in 30 months (yes, 30!) and we were loosely looking at venues. We don't really have a problem booking one now (well, soon), but I feel like 30 months is excessively early for this sort of thing, so I'm sure we'll hold off a bit. I'm not even sure if venues would even take a booking this soon.
How far in advance did you book your venue?
The Skinny Architect: www.skinnyarchitect.com