I am quite particular in my choice of video games…I like multiplayer. I am also a PC (non-console) player. Cloud style gaming is becoming quite a trend in the past year and a half that really opens up the ease of multiplayer games. I jumped on board with the release of the Steam cloud gaming system. They premiered Left 4 Dead, a 1st person shooter where you and 3 other players make your way through hoards of zombies to safety. There are a bunch of different playing styles where 8 players can play in one game. Left 4 Dead 2 came out more recently with the same concept, but a different story line and characters.
The cloud is such a great idea because it allows the player to track their progress in a game, compare their progress to others, purchase games from their site for a discount*, automatically keeps your games up-to-date, and keep the users information/data. All installations of tracking data is stored remotely so that if you change your OS or buy a new computer, you sign in and can download your games without searching for lost installation disks and serial codes. Since your on-line for this capability then why not piggy-back it with games that can run multiplayer? Mind you many of the games often use servers unrelated to the cloud system to host the games (and in some cases can be hosted locally for better speeds with friends). The Steam cloud offers many other benefits like developing groups/friends lists and an IM service where you can see what others are playing if you want to join in to a game.
*The discount price comes with a price. It means YOU own the game. You currently aren’t able to transfer a license to a friend after you are through playing the game. It is essentially and one person use. This has angered many of Steam’s users. But they also run many pre-release specials, holiday and random weekend specials on games.
There are many other Cloud gaming engines around and more on the way. ARS’s article: The future of gaming: up the beanstalk and into the cloud speaks about many of the advancements in this area and a OnLive cloud that is being released to the public on June 17th.
The Cloud system of gaming is also beneficial to the gaming companies because it reduces the piracy of many games. All of the games usually “check-in” with the cloud server that approves the licensing of the game. Because of the reduction of pirated games, I feel that the manufacturers will make more money and should reduce the initial price of many of their games. There are still plenty of games that run about $60.00.
Spooner 
While there are some games that require you to ping a server or even maintain a constant connection to a server in order to play (I’m looking at you Silent Hunter 5), but at present you can play most Steam games offline if you download the full game. Of course games like Left 4 Dead don’t really have a single player mode so I’m not sure why you’d do this!