We just moved our 18 month old ds to a big boy bed. His crib was actually one of those convertible ones where you take the side off to make it into a day bed.
Ds had been climbing out of his crib for about a week, so we decided to bite the bullet.
Surprisingly he has done really well. It has been about 2 weeks now.
Routine, routine, routine....was the key. We kept the same nap and bedtime routines so we had very few problems. The first day or two we had to go back in because he kept getting out to play around in his room. But now he stays in his bed. Only problem is that he wakes up a little earlier than normal to play in his room.
All that being said, I agree with some of the earlier posts that "if it ain't broke, don't fix it". I would have been fine with ds staying in a crib till 2-3 years old, however with him climbing out, it was becoming a safety issue.
Good luck with whatever you decide!!