I tend to always have a can of compressed air lying around. Not sure how, since I'm too broke from buying parts for systems!
I generally only use it for getting dust out of hard to reach places and keyboards.
I've had that super cold liquid spray over a PCB a few times, and apart from making it go all frosty, it hasn't damaged anything once it has gone. When the can is empty, its kinda fun to mess about with it, since its really cold!
Amiga 4000: Apollo Turbo 040, 128MB Fast, 40gb HDD, CD-ROM (needs internet)
C64: 1541U-II, MixSID, WiFi, LumaFix64
ZX Spec, A1200, CD32, MacPlus/SE, A500, BBC Turbo Master (NASA), 2600, Acorn 4000, VIC-20, IBM 5155, GameBoy