Bending wood without knowing how the wood is responding (in a clamp, for example) has not worked very well for me either. After the last few months of learning to bend wood, my best results have been when I've bent wood over my knee or between two supports (like two small trees side by side). I need to "feel" when (or if) the wood is bending easily before I push the limits of the wood. I also found that bending in stages sometimes works better than bending all at once.
The secret the pro's use (to bend windsor chair backs, for example) is to use a steel strap (on the tension side) so that the wood only deforms in compression. Since you can't use a steel strap with most bow designs, just make sure that there is plenty of wood on the tension side while bending. In other words, if you're trying to recurve the tips on a bow with a rounded (or trapped) belly yer askin' fer trouble.
