It is very important to keep your computer clean and free of dust, to stop it looking like this, so get to it. Not only is it ugly, it can damage your components as the heat-sinks get clogged with dust and lint therefore the air from the fan can not freely blow through the heat-sink and the CPU or GPU can overheat. So set a time and take off the side of your computer(s) and give them a clean. It does not hurt at all. This will save you money in the long term, your hardware will not fail early and this will save you money. having to purchase a new CPU due to the fact that your old hardware was killed by the overheating would be a devastating thing to go through if you need your computer to do your work and the computer is regularly shutting down without warning. That is a sign that your hardware is overheating and you need to check the CPU fan. If you have a PCI Express graphics card then you will need to check that as well, easy if you are running Windows, Piriform Speccy allows you to monitor the temperatures of your hardware and see if anything is awry. There is a guide on this page explaining how to setup lm-sensors on Linux to monitor the temperatures of your hardware: http://www.debian-administration.org/articles/327. This will be useful for those who are using Linux and want to take care of your hardware. Another posting about the lm-sensors utility here: http://superuser.com/questions/25176/how-can-i-monitor-the-cpu-temperature-under-linux.
A good way to clean hardware is with a can of compressed air. This is good for blowing the lint and dust out of your fans and the heatsinks easily. This can on Amazon is only £14.97. Ages ago I got hold of a couple of old PS2 mice and I plugged one into my Gentoo box and after a short delay it was working fine, after that I plugged it in and it worked instantly just like a USB mouse, how good is that? I did not know that Linux had PS2 hotplugging but there you go. The only problem I have is that if I mounted a NTFS partition on my first hard disk, I could only access it as root, but that was solved if I re-built the kernel and enabled the FUSE support to mount the drive with ntfs-3g, although if I mounted the partitions on my external hard drive I can access them just fine over USB, but this was just a matter of tweaking and that is something that Gentoo is good at.