I think Buzz is totally worthless and have never used it...
Buzz was poorly thought out, completely botched at launch, had big privacy concerns, and was too tied-in with GMail and you Google profile. But there's one thing I liked about it: the Buzz layer on Google Maps.
That one thing is the only reason I wish Buzz had caught on. See, I'm often someplace where I wonder "hmm, there seems to be something going on over there. I wonder what it is!" I will sometimes search Twitter, but Twitter is atrocious at location stuff, so I frequently only end up narrowing it down to something like a 30 mile area. When Buzz launched, though, I could pull up Maps on my phone and see people who Buzzed about something going on in their location (the location feature was opt-in...at least I'm pretty sure it was).
But since then, any time I've checked, there's never anyone around me on Buzz. A couple months ago we heard these incredibly loud "BOOM!s" coming from somewhere south of us. It sounded almost like thunder but it wasn't, and we didn't see any fireworks in the sky. It went on for about 30 minutes, but nothing showed up on Buzz