Building your own PC is as rewarding as ever. Fortunately, it still makes plenty of sense, too.

It's true that you can't beat the convenience of today's retail PCs. As consumer interest shifts to laptops and cell phones, desktop PC sales still carve out a substantial niche in the market. On paper, they look pretty good. These days, they're fully specified with quad-core CPUs, 6GB of DDR3 RAM, and large hard drives. Many of the lower-end models come with free PCIe slots, at least the ones in regular tower cases.

In theory, a gamer could go with a $600 Gateway, Dell, or HP configuration, and then add a better video card. That would be a perfectly fine PC for most folks. Even for gaming, it would work for a while, providing you kept the extra video card to a shorter, lower-end model that fits inside the case, and that isn't too demanding on the PSU.

But there are also pitfalls to this approach. In years past, PC enthusiasts decried retail PCs, saying that a custom-built model is significantly cheaper and performs better. The first point is no longer true; economies of scale have made it difficult to save money when building a PC on your own. But the latter still holds.

There will always be a place for boutique PC builders that can put together killer, high-end gaming PCs. And laptop buyers have no other choice anyway. But in mid-2010, there are lots of reasons why it's still best to build your own PC. What follows are eight of ours. Have more of your own? Leave them in the comments, or tell us on Twitter at @extremetech.

1. Flexible case designs. Retail PCs come with desktop cases that are more alluring than ever, thanks to sculpted lines, shorter heights, and built-in conveniences like memory card readers and HDMI ports. Few PC users need eight drive bays and six PCI slots today anyway, except for niche applications. But these cases have precious little room to fit an extra video card; you can skip those 10.5-inch-long, dual-height GPUs. That's to say nothing of poor airflow, and—in a few cases—no free drive bays at all. Go with a proper Antec, Cooler Master, or other respected vendor, and you'll never have a problem.

2. Stronger power supplies. Forget overclocking; some of the 250- and 300-watt PSUs that come with box store PCs can't even power a regular video card, unless it's a super low-end model like AMD's ATI Radeon HD 5570. Even if the wattage is there, an extra six-pin PCIe connector might not be. A low-end card would certainly help, but with the prices of 23-inch LCD monitors now below $200, you'll want to play games in higher resolutions—which you'll have no problem doing with an aftermarket power supply and the right video card.

3. Proper versions of retail motherboards. It's usually tough to figure out what motherboard is inside a retail PC before you buy it. But even if the board is from a respected vendor like MSI or Asus, there's a good chance it's a special, low-end version made specifically for the box-store PC vendor. That makes it a royal pain to find additional drivers and support for it down the road—and makes you dependent on the PC vendor. Go with a retail motherboard that's designed to stand alone, and you'll avoid these problems entirely.

4. Quality parts you choose yourself. A retail PC may carry a storied brand logo on the front panel. And if you bought an Intel or AMD PC, you can probably count on that actual CPU being inside. But who makes the parts in the rest of the machine? Often, the vendor's support team won't know, either. That's because from week to week, a manufacturer may switch OEM suppliers for the memory chips, hard drive, optical drive, and other components—all to get the best deal for that batch of machines. Choose your own parts—with our help, of course—and you'll always know what you're getting.

5. No bloatware. Everybody knows about this one already. But we'll emphasize it here for a more subtle reason: It also pollutes the OS install discs that come with retail machines. Assuming you get any discs with your system, that is—which is increasingly rare. Sometimes the OS install files come conveniently preloaded on a separate hard drive partition, but if the hard drive goes, you're toast. Even if you get the discs, that means whenever you want to refresh the machine and reinstall the OS, you'll have to uninstall all that awful crapware all over again—or face miserable performance on what should have been a perfectly clean, fast Windows 7 install. It's a shame that retail PC vendors think your brand new computer is a vehicle to display dozens of ads for its "channel partners," but we'll leave that aside for now. Install Windows 7 from an OEM disc, and you're assured of a clean, fast install every time

6. Coherent support policies. Buying a retail PC means you're stuck with whatever support system the vendor has in place. That was fine 15 years ago, when Micron and Dell PCs averaged $3,000 and came with luxurious phone support. That's no longer the case today. Do you like two-hour phone calls where you're asked to reseat the power cable for the fifth time? Have no problem being told that blowing away the hard drive and reinstalling from the CDs will fix the memory card reader? We suppose it's nice to have one central support destination for the entire PC, if you enjoy feeling like a puppet on strings. If you build your own PC and you know something broke, you can replace it yourself—with whatever part you want, and whenever you want. And in some cases, trying to figure out what the retail PC manufacturer intends for you to do to fix a problem, with all that crapware and weird install discs and special partitions, takes longer than learning how to do it the right way (if you don't already know how).

7. Upgrade whenever you want. This is a corollary to the previous reason. If you add something to a retail machine, like a new video card or even extra RAM, from a different source other than the PC vendor, the company could choose not to honor the warranty when something breaks—even if it involves a different part of the PC. By buying a retail PC and then modifying it later, you're setting yourself up for a possible dispute with tech support down the road. Build your own PC, and you can add a new video card or more RAM whenever your budget allows for it.

8. Building a PC is just cooler. Okay, we'll be totally vain with the last one. But it's true; we'd wager that plenty of frustration with Windows machines involves the bloatware and cheap parts that make up most retail PCs—especially now that Microsoft is finally selling an excellent version of its OS. By building your own PC, you can select quality parts—itself a fun and enjoyable process. And within a few hours, you'll know more about how to fix it down the road than you would have ever learned otherwise.

And did we mention all those awesome games you can play?