Themken: Remember to hoover your computers, at least all openings but better to do the inside too. Pull the power cable, remove the battery and open up but then you must take care not to damage anything with static electicity or push/scrape delicate components. It will be quieter, run faster if the dust had forced it to slow down due to overheating and use less energy.
This is how I discovered what a SFX power supply was. One of my local clients gave me a call about their security system making lots of weird noises. Opened up their out of warranty 1.5U case and found it completely caked with dust. Took a can of compressed air just for the case and another for the power supply. What was weird is that it;s a pretty clean environment with 2 fans blowing air through the case and away from the power supply.
For the webhosting, we blow out the cases once a year. Look for burn marks, bugs, escaped convicts, etc. while doing so. (The datacenter is across the street from one of the county jails.)