In reply to a blog post by Russell Coker about air filters for server environments, I just confirm how important it is to take care of a dust free machine.
In most cases the users won't have air conditioning with filters, but are just using plain desktop machines that are collecting dust. In some cases one might argue that a computer with all of its fans is some sort of air filter by itself, but well... ;)
So, keep your machine and yourself happy and remove regularily the dust from the inside of your machines. For example, I just removed the dust from one of the Debian m68k buildds last week. It was running for about a whole year now without any problem or downtime, so removing the dust was necessary.
I removed the case, the expansion cards and other stuff to get most direct access to the machine. I bought some canned air (spray duster) and blew the dust out of the case. Take care to remove the dust from inside of the power supply as well (of course remove the power plug before opening the case anyway for your own security!). After dusting off with the spray cleaner, I'm always using an old tooth brush to clean the dust from the fans itself. All in all, it's some dirty work and maybe you should do it outside of your house whenever possible. ;)
But in the long run, cleaning your machines once or twice a year prolongs the life of your machines. Some of my machines are now running since 1991 in 24/7 mode. Alas, maybe the reason for some people not cleaning their machines is to raise a nice dust puppy. :-)
P.S.: If you can afford it, choose a compressor instead of compressed air in cans.