Saw there was a hardware forum, and there was no posts either, so here's a guide on how and why you should eliminate dust in your computer.
Dust. We all have to deal with it around the house, almost everyone dusts off their tables, TV's, etc. Not many people bother to worry about dust affecting your computer. Besides the unpleasing visual, dust can hinder your computer's performance, and eventually cause problems for your computer if not taken care of. It's everywhere, on your monitor, in your keyboard, in your computer tower. I'll give a breakdown of the importance of getting rid of it.
A dusty monitor is most obvious and easiest to fix. You get dust on your screen, and you just wipe it off. You can picture what a dust covered screen looks like versus a clean one. There are special rags and sprays you can get for your screen, a normal cloth rag will typically do, but the special ones are better. Avoid the use of paper towels or napkins on your screen, it can scratch (not immediately noticeable but eventually is.)
Your keyboard. You use it anytime you're on the computer, it's out in the open and has gaps between the keys. Dust, hair, and other things can easily build up underneath the keys. Sooner or later the buildup will make one of your keys “sticky”, having it get stuck down or have it move slowly up/down. An easy solution is to keep it cleaned out with some computer dusters, basically canned air that shoots out at a moderately high pressure to blow dust and such out. If it's been over a year without ever dusting it, I would recommend popping the keys out and cleaning the keyboard with paper towels or q-tips. It would also be a good opportunity to soak your keys to keep them shiny and clean.
Your tower, case, whatever you want to call your actual computer, is typically dust gold mine. You have one or more intake fan(s) in your computer that blows air into your computer to help cycle heat so your parts don't get too hot. Areas that receive the most dust are fans. Intake fans, output fans, power supply, GPU fans, processor fans, and any others you might have. Once again, computer duster is the easiest solution. If you haven't dusted out your computer in the last 6 months, you'll want to do this outside. Follow instructions on the duster can and spray out the dust from the fans starting from the highest fan and work your way down, then blow out the dust that has settled on top of any drives and on the bottom of the case.
Dusting out your computer will provide you with quieter fans, better cooling, and in some cases increased performance. I recommend doing a swift spray over of your keyboard and the inside of your computer once a month. If you don't know about computer duster, you can buy them in office stores, some grocery stores, and of course online. I recommend finding one that specifies that it has an anti-inhalant formula., there tends to be a strange smell from the ones that are “normal”.
Liquids. When you use the spray for your monitor, it's usually better to spray it on the rag instead, unless otherwise specified by the spray's instructions. Best to have your monitor off for 10-20 minutes (so it's cool/cold instead of warm.) You can use a damp paper towel to clean the top of your keyboard, mouse, outside of PC case, plastic of monitor, and your table. DO NOT USE LIQUID INSIDE YOUR COMPUTER CASE. For that matter, hold your computer duster right side up. If the can is upside-down then it will spray a liquid, this can easily ruin your computer.
Using vacuums, as Capricorn reminded. You could use vacuum on your keyboard, on and around your computer too. But DO NOT USE A VACUUM INSIDE YOUR COMPUTER. It generates large quantities of static electricity and could fry some of your parts. You can use them on your fans, but better safe than sorry, so you should take them out to clean them.
EXPENSIVE ALTERNATIVE TO GET RID IN-CASE OF DUST FOR GOOD
If you have some money, there's a wonderful thing called mineral oil. It's non-conductive. So you can fill an aquarium with it and submerge your computer parts in it. No decay in performance, temperature is fine. Read here for more info if you're interested.
http://www.pugetsystems.com/submerged.php