After upgrading to 10.1, I could no longer move anything to the trash: I got a message that the items would be deleted immediately.
After a couple of days messing around, I solved the problem. The owner of my home folder (/Users/myname) was root; regaining ownership via this command in the terminal:
sudo chown myname mynameReplace 'myname' with your short user name. This changed things back to normal.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011007113756418