The main problem is that it gets in your tower & clogs the fans inside which can affect the cooling of processor & graphics card.

You can take off the side panel & carefully blow dust out or use a fine brush of a vacuum cleaner to suck it up.

Best way is with pressurised air in a can.
References :

Yes dust will affect your computer performance. But little do I know that dust can interfere your LCD. As far as I concern, the dust will not affect it; the dust will make your fan works harder, that is why you need to clean the dust once in a period of time.
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Dust can build up in the heatsinks and eventually cause your computer to overheat and fry. A friend of mine’s computer wouldn’t turn on at all. Puzzled by the issue, I opened it up, saw the huge dust buildup, blew it all out and the computer booted up fine after that. He was going to bring it to a computer shop and they were probably going to charge him 50-60 bucks for that stupid issue.

Always blow out the dust every month or so.
References :

http://www.youtube.com/watch?v=C6n9A5V4ivg

Vacuuming alone won’t protect your carpet
Even though vacuuming can remove most soil, it is also necessary to clean your carpet on a regular basis to remove the oily, sticky soil that vacuums don’t remove. These soils result from cooking vapors, air pollution, and tracked-in dirt from outside. The particles of oily soil deposited on carpet fibers can cause gradual but significant dulling of colors. The color isn’t lost, but is hidden under the film. If this type of soil is allowed to accumulate, it begins to attract and hold the dry soil.

If carpet is cleaned before it becomes too unsightly, the cleaning chore will be easier and more successful. Carpet in a typical household should be cleaned every 12 to 18 months, depending on the number of residents and amount of activity.

Choosing the proper cleaning system is important. Some systems may leave residues which accelerates re-soiling and defeats the whole purpose of cleaning.

What cleaning system should you use?

Shaw recommends the hot water extraction system.
Research indicates that the hot water extraction system provides the best capability for cleaning. This system is commonly referred to as "steam cleaning," although no steam is actually generated. The process consists of spraying a solution of water and detergent into the carpet pile and recovering the water and soil with a powerful vacuum into a holding tank. This can be done from a truck-mounted unit outside the home with only the hose and wand brought inside or by a portable system brought into the home.

Pergo Regular Maintenance

The surface layer of Pergo flooring is hard and compact, so dirt and dust do not adhere to it easily. The following simple steps are usually all it takes to keep your floor clean.

For general cleaning, use a dust mop, vacuum with the hard-floor attachment of your vacuum cleaner or wipe occasionally with a damp cotton or cloth mop.

For heavier cleaning, use Pergo Floor Cleaner or a mixture of household vinegar and water (1-cup vinegar to 1-gallon warm water) or household ammonia and water (1/2 cup ammonia to 1-gallon warm water). If an accident occurs and a stain remains, you can remove the worst stains with acetone or denatured alcohol on a soft cloth without bleaching or damaging the floor. In a pinch, nail polish remover containing acetone is a handy substitute. Do not use soap or detergent-based cleaners, wax-based products or any type of polish on Pergo floors, as they leave a dull, filmy residue.

There is never a need to wax or refinish your Pergo floor.

***To find a certified professional hot water extraction carpet cleaner, go to http://www.iicrc.com or http://www.pcuca.org***
References :
http://www.shawfloors.com http://www.internetfloors.com http://www.iicrc.com http://www.pcuca.org