I don't think it's actually that many people. None of the devs has reported anything unfixable. Some of the microphone issues seem to have ben solved by rebooting which suggests it's a software issue rather than hardware (which is no help at all to those who keep getting the problem after reboot).

There are more people disappointed because they expected n900 to be an upgrade from n97, when in fact it bears no relation to symbian at all, and is quite different. If that's what you're expecting, you might want to rethink. But I wouldn't let the few hardware issues put you off.