I was taking my CPU out of the box, and when I picked up the fan, I accidentally touched the bottom, and removed some of the grey paste. I haven't intentionally removed any, or cleaned it off thoroughly-- am I still OK to use it, or do I need new thermal paste?
Keep an eye on temps for awhile when running CPU intensive tasks. After you've had the processor for awhile and the thermal paste has 'broken in', run Prime95 and watch the temps to see if they stay in safe levels. Technically, one should never contaminate the HSF/CPU surface with oils from your skin.