I used to pirate PC games. Hard drive got wiped due to a fatal error (due to the downloading, I like to think), started buying games, one of the best computer decisions I've ever made.
Pirating: Takes a buttload of time. Patching and cracking and updating is a PAIN IN THE ARSE. Online support is obsolete. You DO NOT get official servers (so if you wanted to play on 99% of the CoD4 servers, you would need to buy it.). VALVe multiplayer games that are pirated (Killing Floor, L4D, TF2, CS:S, etc.) are serious headaches trying to find servers and updating the game. Takes up even more disk space than buying the game, which is weird because it should be the other way around. Most game mods DO NOT WORK. With multiplayer, most people do not have headset/mic, a good mouse, and a good connection/ping because if they didn't buy the game, chances are that they aren't going to go out and spend money on "ridiculously unneeded" items as such. VIRUSES.
Buying: Game mods. TONS of online support if something goes wrong. A box and instruction booklet (if you're buying retail). Full multiplayer. All the game modes and features. No worrying about cracking and patching. Updating is a breeze. You can play with your friends. Servers LOCATED NEAR YOU FILLED WITH PEOPLE WHO SPEAK YOUR LANGUAGE
. Lots of people have mics and other accessories that most pirates don't bother to own. No viruses. Your settings and game saves stay the same when you exit out of the game. Games are organized on your computer, and are easy to get back if your system crashes. You don't need to worry about your Antivirus or your software updaters catching you and freezing your programs.