Battery Issues with 3.0.1
Another problem I noticed was battery percentage "jumping". I would check my phone, and it would show 15% battery life. As I was using it, the battery percentage jumped up and down between the original 15% and 50%. My friend, who also has a 3GS, has noticed this also.
I'm trying a restore now - and see if that has any affect for today.
iPhone 3GS, iPhone OS 3.0