I generally build my own computers using best-of-breed components (like Thermaltake power supplies). I mostly run Linux, so I can build computers to my own specifications. My livelihood depends on reliable computers.
More and more, I have trouble keeping up with the bewildering amount of hardware changes. Seems like every time I have to build a new computer, almost every specification of internal and external connectors has changed.
Of course, I am becoming more involved in the area of developing for mobile devices, where building my own hardware is not possible. I also have several laptops, both of the Mac and Windows varieties.
Update: In September 2013 I came back to the world of building custom computers. With the introduction of the new Haswell fourth-generation Intel microprocessors, I decided to finally get a powerful Windows machine for software development and testing. Most of the new Haswell-based machines were out of stock, or too expensive, so I made a list of the parts I'd need at Newegg, and was surprised that even with an OEM copy of Windows 8 the total was not much more than the least expensive Asus desktop I had found with the specs I wanted. Plus I got to use my preferred best-of-breed parts, such as a Gigabyte motherboard.
I also built a new Linux desktop for the future, using the case, power supply, and other parts from an older Core 2 machine I built in 2009 and retired in 2011. (This is my favorite case with a carrying handle on top.) So I have two current-generation computers which won't be obsolete for a little while.
This was a great way to learn about the new Haswell architecture, the new UEFI boot process, and so on. The only real surprise was how easy everything was to install. Even Windows 8's install went smoothly, with the install process automatically detecting my hardware and installing drivers. Quite a contrast from the old days. UEFI was easy to use with Gigabyte's motherboard. I simply selected whether I had Windows 8 or not, in the BIOS screen, and had no problems installing Linux.