My '93 Trek 5900 has most of the original titanium components -- Ibis stem, American Classic seat post. I'm not sure but I think at least some of the bits in the King headset and White bottom bracket are titanium. Pretty nifty, but probably not much lighter than aluminum. I just replaced the ridiculously long Ibis stem with an aluminum FSA stem. I don't have a scale but they felt about the same weight, although the FSA stem looks much chunkier. The Ibis stem is slender and elegant.
A titanium bike is on my wish list. I don't care whether it's lighter or faster. I just want one.