With 10.6 - 10.6.1, my MBP was running noticeably hotter and louder than Leopard. My June 09 15'' Macbook Pro is now running much cooler, I put my hand on the sides and there us no longer any heat. Snow Leopard is out of beta.
10.6.2 is driving me crazy, I shouldn't have upgraded and I'm thinking of rolling back to 10.6.1. I was thinking I'd be ok since I never had any of the same problems that most other people had but now it just "f-ed up" running slow, various apps are crashing, it seems my cpu never just idles anymore, and Flash has almost been a complete disaster. I'm glad things are going well for you though.
I know you've probably already done this, but I might aswell say it: Repair Disk permissions, restart the Mac and see how things go.
Oh yes, many times, I'm still trying to work out a few kinks, I'm kinda mad though since it was working fine before.
10.6 ran fine for me. 10.6.1 was good for a while but then a CPU bug would pop up and heat up pretty good. 10.6.2 seems to have fixed that and is running cooler.
That's interesting, I didn't use 10.6 straight up but 10.6.1 seemed ok, not great but ok, 10.6.2 is where I'm having problems, looking around I'm finding that the recent Safari update is screwing things up or at least bringing the problems out of the woodwork. I'll get a fix going and see.
have you used onyx before? if not download it and run the weekly and monthly script packages, almost ever mac never runs them because there not online when the script would normally get executed, those script packages clean up the mac and make it faster by clearing out old log files and temp files. then repair disk permissions after that.