I assume you've read the news that's been plastered all over every gaming site for the last couple of weeks: Infinity Ward announced it would not release a dedicated server for Modern Warfare 2. On the heels of that, John Carmack made a similar announcement for Rage.
People who cut their teeth on console multiplayer are having a hard time understanding why the loss of dedicated servers is such a big deal. After all, consoles get along just fine without them, right? Even some PC users are having trouble grasping just what we're in for, and they wrongly imagine that PC multiplayer is going to start looking like console multiplayer. It isn't. It can't.
Here are the problems we're about to face:
The biggest problem is cheaters. On a PC, you can run anything you want. You can reverse-engineer the network protocol, write new software, and run it at will. That just isn't possible on a normal console. Anyone hosting the game can make any changes they like to the game state, at any time. Infinity Ward has promised to ban cheaters, ignoring the fact that fighting cheaters is much, much harder without trusted dedicated servers. Even games like Team Fortress 2 must be updated regularly to keep the cheaters from ruining things for everyone. If the games were taking place in the anarchic wild where every accusation of cheating comes down to a battle of he-said / she-said, then diligently fighting cheaters becomes an expensive time-sink.
2. Unstable Hosts
PC's don't have standardized hardware. On the Xbox, it doesn't (much) matter who hosts the game because everyone has the same hardware. Ignoring bandwidth problems, anyone can host the game as easily as anyone else. But on the PC, who the host is matters a lot. Computers are not all created equal, and figuring out if the 3Ghz dual core machine with 2Gb of memory running Windows 7 will make a better server than the 2.0Ghz quad core with 4GB of memory running Windows XP is a really tricky question. More to the point, some machines may have fast hardware but be bogged down with horrible, lag-creating software running in the background. The matchmaking service might run a little test to try to figure out which machine is the "fastest," but this can't take into account programs that cause periodic performance spikes.
3. End of the Server-Based Community
The end of dedicated servers means the end of the communities they supported. On the PC side, lots of people frequent favorite servers. The servers act as a meeting place and a hangout. They have forums and regulars and moderators. People form friendships and rivalries, clans and communities; none of which is possible in games based on friend lists or random strangers. There is an entire multiplayer culture that is being abandoned here.
4. Lack of Standardized Community Tools
On your Xbox 360, you have built-in friend lists and the like. The PC doesn't have this. Microsoft is trying to make that happen with Games for Windows Live, which isn't yet robust enough to really rival its PS3 / Xbox 360 counterparts. Worse, not all games will support GFWL. On the PC, there will likely be several competing and incompatible systems all trying to fill the "gamer community" niche. Steam and GFWL are the two big ones, but there are smaller ones and I'm willing to bet there are more on the way as publishers scramble to build the One Content Delivery & Community System To Rule Them All.
We're losing the PC style community (which was based around servers) and in return we're getting a balkanized system of friends lists strewn across different publishers that all have their own little program running in the background.