It's only obsolete to the leet gaming crowd who are running the SLI w/ an FX60 and 2GB of RAM. Until just recently, I was running a s754 A64 2800+ @ 2.4GHz on an MSI K8Neo Plat w/ a 6800GT, and it was awesome. Because I was able to upgrade for no cost to me, I went up to a s939 Opteron 146 w/ 2GB of RAM and a 7800GT, OC'd the Opty to 2.8GHz, and it was a nice piecemeal upgrade, but to be honest, the difference isn't as stunning as I was hoping for, probably because I was already happy with what I had. I passed my old hardware onto a friend of mine who was running a P4 1.8GHz w/ a Ti4200, and he's thrilled to be able to play all the newest stuff at 1024x768 or higher now.
If we judge our rigs based on what Maximum PC calls 'obsolete', then I'm pretty much already there, and I just upgraded like 2 months ago. From a practical perspective, my son's AthlonXP 1700+ w/ a Radeon 9600 and 1GB of RAM plays games like Battlefront 2 great with most settings maxed, and games like CoD2 well if you lower the settings to medium. His is a MAYBE $300 desktop, and he loves it. PC gaming isn't exactly flourishing right now, so any significant upgrades for gaming are for 1-2 games that will be out this year that are worth playing. Of course, if you haven't played a lot of the awesome PC games that are only 1-2 years old, like FarCry, KOTOR, the original Battlefront, etc., you would be well served with a $300-$500 budget PC that will run these games like butter in most cases.