All of a sudden today, my the mouse cursor started jumping to the exact same spot on the screen (near top-right) every second.  I could move it for up to a second, but it would jump back.

I have a Logitech mouse.  Unplugged it.  Still does it.

Restarted computer.  Still does it.

Tried Magic Mouse.  Still does it.

Gaa!!!

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Found a forum post https://discussions.apple.com/thread/1829111?start=0&tstart=0

Someone mentioned Wacom tablet.  Yes!  I have a Bamboo Drawing Tablet on the side of my desk.  Someone bumped the pen so it was setting on the tablet.  Each second, it was moving to the position dictated by the pen on the tablet.

Moved the pen.

Everything works.

Hope someone finds this and saves them a headache or 3!