It took hours to upgrade, but it was relatively painless.  I was surprised to find all my desktop icons still there.  I ran a couple of my games, iTunes and applications.  Everything seemed to work.

I'm still looking for problems because I don't trust upgrades (even Linux upgrades).  I have to say, the only thing I see so far is things are a little slower, but that might be because everything wants an upgrade and is accessing the web.