How high of a pressure do you need? 30-35 on the street, 5-20 on the trail. I like rubber because they'll flex when tweaked by a rock, where metal will break. Somebody once told me that metal ones are more prone to leakage than rubber; I can't remember who it was or how true that is, but I did have a leaky metal one that you had to fiddle with a bit and tighten the cap to stop it from leaking. Metal does look nice on mall runners though.
yeah metal ones do leak. You have to regularly tighten them. As far as pressure is concerned I don't see why you need to run your tires at 90 psi. It's also real easy to catch a metal one on a rock and either rip it out or smack it in and bust it. Rubber valve stems will actually bend when hit, but metal ones just go shooting straight back into the tire.