Sounds like maybe a nipple gall or bladder gall. It's a deformity that some trees have a predisposition to - it is more cosmetic than dangerous to the trees health. It is the kind of thing plant breeders would try to eliminate if they were breeding some new variety. I believe it is caused by an insect laying an egg and getting the plant to alter it's DNA so that a protevtive covering (the gall) is provided for the developing larvae.

EWE! well I appreciate your help, I noticed the other day there are lots of leaves still on the tree with those parasitic things on them. I'dlove a good excuse to radically prune the tree.

PL