Non-factory Apps Disappearing Randomly After Upgrade to iOS 5.1

Hi all, I've had my iPad 2 for about 9 months. Since upgrading to iOS 5.1, on two separate occasions, I've had all but the factory apps disappear from my iPad. This happened randomly during the day, not during or immediately following a sync. My most recent sync for my iPad was on 3/14, 6 days ago. I had been using my iPad throughout the day, then unlocked it this evening and everything is gone except the factory apps, i.e. FaceTime, Messages, Reminders, etc. All my media is still there, and all my settings are unchanged (email accounts still working fine, movies still there in the Videos app), but all downloaded apps are gone. No games, none of my work apps, nothing. This is the second time this has happened since I upgraded to iOS 5.1 about 2 weeks ago. First time was the day after. Last time I did a full wipe and restore, hoping it was a one time glitch. I've done some searching, and the only other instances of people's apps disappearing that I've been able to find were related to syncing. I have the latest iTunes, all software is patched and up to date. I have syncing via WiFi disabled, as well, it only syncs via cable plugged into my home PC.

Hoping someone else has seen this or has some idea.

(My battery life is significantly reduced after the iOS upgrade as well, with no changes to settings or new apps. I get a day or two of light use before I'm down to 10%. I was at 30% in the morning when I put it in my bag, and it was dead when I took it out later that afternoon. I used to get a good week between charges.)