I have a feeling this has to do with the ninja fix to "trick" the Intel Drivers for performance.
Basically, opening Minecraft will inconsistently (sometimes it happens, sometimes it doesn't) open up 3 javaw.exe processes viewable from the Task Manager. Normally, it opens two; the javaw.exe for the launcher and the javaw.exe for the game. This
third, fake process eats CPU usage and memory like...well to be honest the only analogies I can come up with are either offensive or so out of mainstream culture so...basically at it's worst, the fake javaw was using 96% of the CPU and over a million KB of memory. It has since died down this behavior and capped itself around 800,000 KB and 25% of the CPU, but this is still a lot. Ending the fake process does nothing visible to affect the game.
Attached are screenshots of my Task Manager.
Edit for August 1st, 2013: I have so far been unable to reproduce the fake javaw process. However, I have identified that the one eating the CPU isn't the fake process, but the launcher.