PC gamers won't like this.
One of the greatest things about PC gaming is that people can set up dedicated servers for multiplayer matches. None of that silly peer to peer stuff that might give the host an advantage, not to mention that dedicated servers typically have connections that are capable of supporting a greater number of players with smooth and stable results.
Unfortunately, it seems that Modern Warfare 2 won't be having any of that. Joystiq heard on the from Infinity Ward's Ryan Bowling on the Bash and Slash podcast that matchmaking within Modern Warfare 2 would be reliant on proprietary server technology (called IWNet), and wouldn't allow users to host their own dedicated servers.
While those playing COD4 on the Xbox 360 and PS3 have plenty of fun without the need for dedicated servers, there's still a lot to be said for having dedicated clan or local servers where everybody knows your name.
On the bright side, the PC version isn't delayed.

I never had one. but its already saved me the money!
Lets make sure this does not kill PC MULTIPLAYER!
http://www.petitiononline.com/dedis4mw/petition.html
even cod1 is still going for pc. why do this?
they are gonna make us play on their servers and their leagues... whats next? we have to join one of their clans? ... :@
http://www.youtube.com/watch?v=1FKty5Kpf4w
They have learnt from the consoles that if you control the network on which people play you can get more money from them, they have created the IW.net for this very purpose. You but the game (now at an over inflated $60 for less features) and start to play online. some 8 weeks later the release DLC with just 3 new maps and maybe a spec ops mission, and charge you another 10 bucks for that. You can refuse to pay of course, but then you cant join any games on the match making service because they are all playing with the new maps, so you begrudgingly pay, then 8 weeks later another DLC and so it goes on and on
in the end your game ends up actually costing you $120, it is all about screwing you over and bleeding you dry