lapping a P4

I've just purchased a P4C D1... I've noticed the heatspreader is far removed form being smooooth. is there a reason why I shouldn't lap it?

There's a lot of articles about this under the front page. Opinions on this vary somewhat. The heatspreader probably flattens out some under pressure from the heatsink. Lapping it might help, but in most cases it won't get you more than 1-3C. It might be a good idea to try running it for a while without lapping to see how your temps are (and to make sure it works).

Being smooth and being FLAT are 2 very different things. I lapped my 2.6C down to the copper and saw absolutely NO improvement in temps.

I wouldn't touch it since you've just purchased it, and if you damage the chip will lapping it. You can't RMA it. See what your temps are first.