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Immediately after installing Lion I encountered the problem and have been researching it since. I thought I had fixed the problem by turning off pointer acceleration, but unfortunately that just reduced the symptoms.

My experience:

I first noticed that my mouse pointer will jump around the screen while moving it. That is, I would move the mouse a short distance but it does not move (seems “frozen”), then appears on the screen having covered a greater distance than it should have (100px move, appears 250px away [arbitrary values]), with no movement animation.

This seems to happen when various components in my system are under some sort load. It reminds me of older PCs and how human interface devices would take a back-seat when the system bus became overloaded.

I have noticed the problem occur during the following system activities:

  1. Dropbox displaying a growl notification about files being removed from my system (Growl, video, disk?)
  2. Saving out files in photoshop (video?, disk)

What I know it is not:

1. Solely Disk I/O related. I have run a command like “dd if=/dev/random of=/tmp/largefile bs=1024 count=4000000” and moved the mouse all around the screen.
2. Solely video-related. I can play games just fine, though the pointer does become noticeably more jumpy.

I expect the problem is related to multiple components.

My current system configuration:

  • 21″ iMac (Mid-2010)
  • 8GB ram
  • Additional 20″ monitor (mini-to-dvi adapter)
  • Logitech MX518 mouse
  • Apple USB keyboard
I’m going to continue revisiting this until I’ve figure out what’s causing the problem.