In reply to peter k: I usually find that i dont eat that much when i'm out climbing, one of the reasons being that once i stop climbing and have a break i usually find that i go off the boil (so to speak).
This is a double edged sword because you know when your climbing crap you try a little harder, then you fail more and then you get all frustrated!!
I usually find that all my technique goes out the window and then just thug my way up the climb in such bad style.
What i find works for me is when you start climbing after a break is go and do something very easy say 3 or 4 grades easier than your best grade. It just takes the pressure of you as well especially if your leading. Failing that go and do a route that your very familiar with, this will put you in the right frame of mind for climbing well.