Expose/Hot Corners not working

I love, love hot corners, it makes my work go so much faster. After installing Snow Leopard I notice that my hot corners just sometimes don't work. I check in System Preferences and my hot corners are set up, but they just won't work. It is so frustrating, i was just in the apple store last week getting a faulty battery replaced, and would prefer not having to go in again. Any suggestions? I am working on an early 2008 MBP. Thanks!

After upgrading to SL, my corners still work fine.

I know this may sound like windows troubleshooting, but try this:
- disable corners
- reboot
-re-enable corners

Any difference?

I already tried this. I worked once but hasn't worked since...

Have you tried logging in under a different user account?

I just added Snow leopard to and I am having the same problem... Someone suggested booting your computer in safe mode... going to try that but not really sure if thats really going to do much.