I use liquid pro and get on well with it. I've not managed to quantify temperature improvements, as I changed quite a few things at once when "installing" it. However there are reviews online which do a better job of this than I could.
Broadly speaking I agree with rjkoneill on this one. However, if you can be bothered with lapping both the cpu and whatever you're mounting to it, and you don't care if the cpu ends up firmly attached to the heatsink, then go for it. It'll beat paste if it's installed correctly.
If you're going to thoroughly clean the block with acetone, but not lap the surface, then don't bother as you're not going to get better results. There's still grease in the pores of the block however obsessively you washed it, and this doesn't mix well with the liquid pro. You end up with copper - grease - liquid pro - grease - heatsink, which isn't going to perform measurably differently to grease alone. As shown by the various reviews which ignore the directions to grind the surface before starting.
Note that waterblocks and heatsinks tend to be deliberately bowed to ensure contact in the center when installed. Lapping a bowed waterblock is bloody difficult, and the results can be worse than before you started. Rjk and I both have a machined flat ek supreme, and I don't think either of us are particularly impressed with the results.