Interesting. I've also met Jenson Button and he was really nice. Spent a lot of time being friendly. The person I'm not keen on is Jason Plato who always comes across as really smug, but I know a couple of people who say he's great. I think it just comes down to who you meet on the day.
Jason Plato definitely has a not-nice side. I received a rude and unnecessary email from him once after criticising something he'd done in a BTCC race on a blog I used to have. I assume it actually was him.
How long ago did you meet Jenson? He used to be really down to earth and pleasant, it's since his world title that he's disappeared up his own bum a bit.