I've just painted my uprgihts and managed to mask the bearing hole, but wasn't quite sure how to mask the machined tapers - masking tape was never going to work and I didn't want to have to try chipping the paint out afterwards. So, after a little investigation, I found some stuff called maskol which is primarily used by model makers, but works perfectly well for masking taper bores. You just paint it on and leave it to go dry (few minutes) and it leaves a rubbery coating on what you paint it onto, you can the paint the part without worrying about the taper. Once you're done, you simply use your finger or a screwdriver to peel off the maskol, and you're done, nice clean tapers.
One thing to bear in mind is that maskol is soluable by celly thinners, so if you have excessive thinners in your paint it may wash it away. I didn't have any problems with this though, and I was using a reasonably thin mix.

Kingr

With a little care petroleum jelly (Vaseline) or heavy grease can be used to the same effect.

Mick

Maskol is basically just pva glue, which maybe cheaper.

Cheers

Chris