As Ashton said, it's my understanding that CV joints make more of a clicking noise. This BMW site call it a [link|http://www.autohausaz.com/bmw-auto-parts/bmw-noises.html|hum] when a wheel bearing is going bad. I wouldn't use that word, but it's close.
The noise is noticable when turning at low speeds, like turning into a driveway. That puts more stress on the bearing than driving straight.
I too have heard horror stories about bad wheel bearings causing wheels to fall off, etc. I don't think this is anything like that bad - it's just annoying. If it were a RWD car, changing the bearing would be trivial. But since it's a FWD car, one has to remove the lower control arms (disconnecting various ball joints, etc.) to get at the bearing. :-( Coupled with the difficulty in being sure that that's the problem, we've been hoping that it'll just not get any worse. It has literally been at least 100,000 miles with this noise.
I probably should try to get it checked out one of these days...
Cheers,
Scott.