I've noticed this a couple of times recently, leaving a program, I get the wallpaper, and no icons, phone appears frozen. Also have had an open folder have it's window disappear, pressing the folder icon has no effect, as the OS knows it is open already.

running the official 2.1, not rooted, no recovery.

 

I too have had this happen. Stock 2.1 running tag home. No root, no custom kernals.

 

happened to me this morning when i was updating weather widget for the trillionth time. (why does a weather widget need to be updated twice a week?) All my screens were empty short of the live wall paper. I pulled the battery and got back going. I did have to re-load the weather widget however.