I have to add a couple of PCI cards this weekend, so I’ll get a chance to take my motherboard tray out. It’s really nasty from smoking and just dust and grim. I would like to use this chance to clean off all the cards, motherboard ect… But I’m not sure what cleaner would be best, and would not damage anything. Would rubbing alcohol be a good choice?
Um…I’ve been in computers for years…I think a little vacuum for electronics or compressed air (from a can, not the industrial machines) should clean it sufficiently. I usually stay away from liquids even if they have serious evaporative qualities.
Second’s talking about smoke tar. Dust bunnies (the only problem I have - but with 5 machines it’s a problem) should be dealt with using compressed air either outside, or someplace you’re vacuuming soon.
Note that using a vacuum directly is not a good idea. They tend to generate static electricity which is a Bad Thing.
I don’t see rubbing alcohol being a big deal. (Touch the case to ground yourself with respect to it first.) It’ll probably be difficult anyways - where there aren’t components you have to clean around, there are soldered bits that stick up and tear your cleaning rag. 
I smoked next to my last computer for 3 years, most of that with the side off. I never had any problems other than some discoloration. So unless you, your cig and your computer all live in a closet, you should be fine. Just get a can of compressed air that is designed for this kind of thing and you should be good to go.