Had the same problem:
- Random Crashes
- Applications not responding
- Freezes/Locks Up's
- Random reboots
And was getting the "force close/wait" message frequently
. I found out that it was a Live Wallpaper that I downloaded from the Android Market
that was causing the problems. I uninstalled the Live Wallpaper, Formatted the Memory Card and Hard Reset the phone, but some problems still remained.
So i purchased a Micro SD Memory Card Adapter
and formatted the Memory Card using a PC instead of using the phone, and since doing that, i have had none of the problems above...