Mouse pointer intermittently jumps to corner of screen
The mouse problem you are suffering from has to do with OS X polling rates. It has been a known issue for quite some time now. You can read about the issue and a general rundown of some of the mice affected.

Note that contrary to what the author states, the problem still very much exists in OS X Lion. Refer to this post for your specific problem, which identifies CPU cycles as a possible culprit.

As a designer, I found this insufferable. I purchased and tested (even Apple's Magic Mouse) numerous mice only to have them returned to the store. Each mouse worked flawlessly under Windows 7 I might add. I ended up buying a Razor DeathAdder (Black Edition) with ample DPI and polling rate (even though I don't game). It still jumps every know and again when the CPU is busy (I'm running a more than capable Mac mini 2.3 GHz i5 with 8 GB of RAM and an OCZ Vertex2 SSD) but the jumps are so extremely infrequent that they are now a rarity rather than the norm. I should note that this problem occurs using the native OS mouse drivers, the Razor factory driver, or SteerMouse.

Sadly, there is truly no solution, just workarounds (mine was to buy a mouse with industry leading polling rates and DPI.

The simply truth is there is a flaw in OS X and how it handles mice that needs to be fixed. And Lion has not corrected the issue.