ORIGINAL: mobow
I used one for a few years. They suck in the winter w/ gloves, so I stopped using them. It's never been a problem. If you grip and form are right, the bow isn't going to jump out of your hand anyway. It'll stay there.
I think it's more of a mental/subconcious thing than anything. Mine has never jumped out of my hands either, but I know Rob had to make a mental effort when shooting my Ross without one (he shoots with a sling).