Linux is great for me. My office PC is old. It's a 450mhz P3, 10gb hard drive, with 128mb of RAM. I added 128mb of RAM to make it 256. Normally this PC would run windows really slowly, but with Linux installed, it's not too bad at all! Plus, it is free. It is great because I get a whole slew of amazing, free, open source applications available right away... OpenOffice.org, Thunderbird, Firefox, Evolution, Gimp, etc... It's also incredibly stable. It was running W98 on it before, and i'd much rather haver paid $25 for more memory than a hundred bucks or two hundred bucks (not sure what the upgrade cost is these days) to get XP on an old, slow machine.
I much prefer the environments of Linux (xfce, gnome, kde) in reference to Windows. However, you mentioned gaming. For gaming, you're going to want the best drivers and the best everything for your PC. So if you want to game and use linux, a dual boot option might be best.
the reason I switched was because I couldn't stand MS's bloated OS and because I had an old PC. If you have no reason to switch, probably not worth the hassle... Then again... it's really fun to play with. Maybe make a small partition on your harddrive just for playing with Linux? Some good distros to try are Fedora and Ubuntu. I use Fedora.