After changing my motherboard it meant that I had to remove the 3570k that I de-lidded. I was surprised at how staining the liquid pro has been.
I had use it on both surfaces of the IHS. The copper bottom of the CPU cooler was quite stained and patchy and the lid of the CPU has stained so that you couldn't easily read what is written on it. The underside of the IHS (above the core) is discoloured slightly.
It took quite a bit of work to get the surface of the CPU cooler to be stain free again (still not perfect), I was surprised at how much it must have penetrated. I thought that it didn't have an adverse effect on copper..?
I have removed the liquid metal now (too messy to apply easily) and instead used this...
https://www.overclockers.co.uk/showproduct.php?prodid=TH-000-GD
...it is very easy to apply and the overall temps seem about 3 or 4 degrees higher at most.
The liquid metal pro is a superb TIM in its cooling capabilities but in use it can be difficult to apply and if you should ever drip a small amount on your board you can have real trouble in removing it. I was quite enthused about it at first but I just couldn't see myself using it again.