Hey Achilles, contact cleaner is meant to clean the carbon buildup on electrical contacts (switches) eg: contactors, isolators. Rotary switches etc. before a contact fully closes there will be a slight arc of electricity between the contacts and it will cause carbon residue to build up.
Definitely NOT good for cleaning dust out of your pc, although I don't think that it would harm your pc - contact cleaner is not usually flammable or conductive it would probably leave some sort of residue, and would not provide any benefit... You are better off getting an air duster. This is an example of one: http://www.bunnings.com.au/3-in-one-professional-350g-a...
Ignore the price Etc and this is in Australia. I know the cost on this is about au$6 so you can get it pretty cheap if you look around.
thanks, my step father used it for cleaning the dust out of a stereo reciver and then used canned air and it blew out a bunch of cold air and froze the contact cleaner. deffinetly not using this stuff.