...thing is, if it's in tabs, only the people interested in keeping up with the global chat will opt to distract themselves with it. and for everyone else, it'll largely be the same.
and I don't see it any more distracting as having to chat with a player that doesn't have a mic.
really I don't care about having global chat too much, I wouldn't use it hardly, but I support the ones that want it - I don't think it's a bad idea if implemented correctly.