Our program didn't have night float, though the internal medicine program that our residents worked in did.
I think its a good idea. Doing night float creates a different type of work environment. IMHO a key to better psychiatric training is mastering different clinical situations. It also allows the majority of residents to have a better quality of life, while allowing the residents stuck on night float to get those night hours out of the way while having their circadian rhythms adjusted for it.
The only problems I've seen is the resident going to night float is going to have a wierd adjustment for the first few days going in & out. If your program doesn't have too many residents, it won't be able to rotate this among a large amount--forcing residents to rotate this quite often. That'd be a negative for going to night float since you want residents doing it at a minimum.
Another problem is the night float residents have to have a very good plan of communication & safety planning in terms of who can handle the emergencies. E.g. 3 IM residents did night float, what if there were more than 3 emergencies at once? Rare--but it can happen. You have to make sure the number of residents on night float are of a number where the number of emergencies at once will not realistically overburden the residents on hand.