My desktop is really clean, actually. Not many icons.
Just froze again. Sigh. This time, I was organizing my email (via Mail) and was trying to put something in the trash. "Trash" was off-screen -- usually I just drag the item to the top of the screen and the screen moves until I can see what I want, than drop it there. This time it got "stuck" at the top of the screen. The rainbow pinwheel turned for a while and I hoped it might pull through (become un-stuck) but nada.
Since OSX treats each icon as a window
While my desktop is clean, as I mentioned before I used to use scads and scads of windows (now I use tabs). Could the scads of windows have caused this problem? (And if so, how would I fix it? More memory?)