I recently bought a used early 2008 MacBook. It is in decent shape, has a couple small bits of plastic around the palm rest and one one side of the LCD missing. Battery life was so-so with it. I Decided to go ahead and buy a new battery and now it gets 4 to 5 hours of battery life. Installed OSX Lion on it as well, put a 500GB Hard drive in it. Also was given a free wireless Mighty Mouse to go along with it.
I decided to check out the situation of the thermal paste as I noticed that it tended to run a tad bit hot and the fan kicked in quite often. Upon removal of the CPU heatsink, I noticed that there was basically no thermal paste left. I went ahead and cleaned the CPU off and applied a fresh coat of Arctic Silver 5 to it. It doesn’t heat up as much as it did. Glad that I did that when I did because I imagine I just helped give the MacBook more of a lifespan.