My Moment began locking up 2x per day recently. The only way to restart was to remove the battery. I haven't been able to find a solution anywhere so I wanted to post my findings.
I had Advanced Task Killer (aka ATK) set to automatically kill everything every 30 min. I tried reducing the settings to safe and back to manual kill, but to no avail. Then I came across this article
http://androidforums.com/motorola-droid/18334-task-killer-apps-truth.html, as well as others, and uninstalled ATK v1.9.3. My phone hasn't locked up in 3 days and battery life seems similar to when I constantly 'killed' apps. I'm running Android v2.1.
See if that helps.