CoD 4 is really bad when it comes down to punkbuster. It seems the software doesnt really help at all. I also remember that i was playing for a while when my friend decided to borrow my disk to play 'single player'(he said). Then, we actually met online(he invited). With the same CD-Key( i realize later). I made him uninstall and I havent played since then.
Apart from whizzier graphics the later versions are pap, and you have to go via the awful matchmaking. Running your own servers and LAN games are a basic right!
Still playing CoD4 MW once in a while. It's just about the right kind of game for my MBP 2009 (GeForve 9400M), playable with good graphics. As stated earlier, there are LOTS of servers, it's still hugely popular. 🙂