I too use compressed air (at around 90 to 100 psi, via a small metal tube nozzle) to clean out PCs and dirty test gear. Both to remove dust (with extra scrubbing using a paint brush if necessary) and also to blow dry boards after a soap and water wash if they were *really* dirty. Compressed air blast is the only way to get water out from under VLSI solder-bump mounted chips, for instance.
Never had any problems. I don't count the time I deliberately spun up a squirrel cage fan until it exploded. Just bear in mind that the air jet exerts physical force. Would you press the thing that hard with your finger? If not, don't hit it with the air jet. Standard fans can easily be spun up till they break. But even before that point, they contain coils and magnets, so can work as generators. How much AC signal from the coils is safe for the fan internal circuits? Best to hold the rotor to prevent it going really fast.