Same issue here, with a 3.4Ghz Core i7, 1GB video card and 16GB of RAM. Issue started with Pandaria. Stuttering mouse pointer, slides all over 10x further than I actually move it, and it only happens inside of WoW... with WoW running and jittery, i can swap to a browser and my mouse resumes normal function, swap back to WoW, sliding all over the place, jittery...
For me, it seems to creep up, along with sound effect stutters/stops/starts and framerate drop during even a single Urol's Vortex, or getting a mage buff.... but throw out hurricane, blizzard and a few fan of knives, no problem... usually.
Then on some boss fights it's like time will slow down and stretch, then snap with all damage taken and dealt out slamming into the span of a single sec, and i'm left staggering around wondering wtf.
Issue only happens in WoW. I've done a complete erase from system and reinstall from Blizzard of WoW's client. I've tried it in 64-Bit and 32-Bit mode, with the issue happening slightly less, but not less often enough, in 32-Bit as opposed to 64-Bit. The issue occurs in battlegrounds, large raids, cities, farming bfe... doesn't matter.
Resetting my SMC and doing an immediate PRAM reset affects no change. Going windowed sometimes help, sometimes it doesn't. Restarting my machine helps sometimes, other times not.
It's just all so flaky, anything could cause it to happen, and other times things that would otherwise cause it to happen fail to.
I've called into Blizzard phone support and talked with a fellow for an hour, who then suggested we correspond via email; I sent him an email on my system profile but have never heard back from him.