Originally Posted by oralpain
Lapping is a very good idea, for many heatsinks, but having a mirror finish won't help in the slightest.
I only lap to 600 or 800 grit, sometimes its rougher than the original finish, but every time I get noticeably better temps. Why? Because the heatsinks are now flat.
As others have said, a little roughtness won't hurt anything, with a good thermal compound. However, if the heatsink is not level (concave, convex, ridges, ect), no thermal material will make up for it.
Flat trumps smooth.