One thing that is disappointing nowadays is that it's tough to learn how to build PCs. The upgrade paths for many pre-built computers is not terribly obvious or cost-effective. You buy a nice machine, and find out that it uses a discontinued line of CPUs or can't handle the voltages for the latest cpu. Or it only has 2 memory slots and you have to toss out the old ram to get new stuff. Or they left off the pci-e slot. Or even if there is a pci-e slot and you want to make a substantial upgrade, the case is 3 inches too short for the latest video cards. And worst IMHO, are computers sold with cases that will not accept standard ATX motherboards.
That's how I and most others learned, but I was lucky and my first computer was built by UNISYS under a special contract with the USAF Academy. The computer used a SCSI bus and several business-grade components and the only thing non-standard about it was the ram was soldered on the mobo and the mobo had a special memory bus slot for ram upgrades. Of course that special memory card was not sold to us, so to add more ram we used ram expander cards that slotted into standard 16-bit ISA slots (yea, that's slow, but it was the only way to get some software to run). Upgrading that computer one step at a time, starting with another hard drive, going to more ram, putting in an ISA hard drive card and ISA hard drive, plopping in a math co-processor, getting one of the first "windows accelerator" video cards, adding a soundblaster "pro" (skipped first soundblaster and adlib cards due to a monthly salary of $60) going to one of the first AMD "clock doubled" cpus (one of the first lines of cpus with a clock multiplier!), and finally going for a new mobo to start clean, was how I learned to do everything. By the time I discarded that old case, I was pretty damn good at linux, networking, windows 3.11, dos, could work my way around in a sun workstation, and was familiar with almost all conventional hardware configurations since I'd tried them all.
When I had the money, I treated myself to a premium pre-built computer (anyone remember Zeos? Damn good computers) around the time CK hit public beta, and I splurged on 32 meg of EDO ram, one of those spiffy S3-968 video cards which gave an astonishing 640x480 with accelerated 3D graphics in CK, and it was in a huge case that the magazine reviewers said was a model of upgradability. That case lasted about 4 years, and it was the last time my main computer was pre-built.
It's hard to do that today unless you buy from a boutique shop and get parts that you know up front have an upgrade path.