I know what probably went wrong. I think it's the same thing that went wrong for me.
I had syncing set-up between Outlook, G1 and Google Calendar. But imagine this scenario:
1. Google Calendar Sync runs every 120 minutes.
2. The G1 syncs every 10 minutes (theoretically)
If you create any tasks on the G1 within one of those windows where the calendar sync runs before the G1 sync does, I think it might somehow tell GCal that all is well...so then GCal will assume that the device is reporting deleted tasks and tell the device to delete them.
My solution is to switch GCalSync to 1 way now...only GCal to MS Outlook. I hope this solves my problems, lost a few tasks and then was like whaaat?
Oh yeah. The G1 rocks!
k