I'm still skeptical on this, but apparently OnLive is a browser plugin that can bring any supported game (there aren't many at this point but the ones they have are 5 star titles) to anything with a screen. This includes PC, Mac, TV, and even cell phones. The specs are low: for PC you need Windows XP or newer; Mac you need an Intel based machine with OS X; and for TV it says you need an HDTV. The best part of it all is that everything is instant. The only download is the plugin. All games are stored on their servers, so when you start the game it pops right up. The TV isn't supported right out of the gate though, you'll have to wait for an undisclosed amount of time to purchase their "microconsole."
For $14.95/month, I'll probably pass as you still have to pay premium prices for the games as well. However, they are planning a free service that allows for renting games and downloading free demos. This is basically just a way for users to test out the service to see if they like it. I would be more apt to use this service and just rent a particular game for a short while than pay $50 for a game that I may lose should the service ever go under. I shutter to think of how much money I will have lost if Steam ever shuts their doors. Read more about it here:
http://blog.onlive.com/2010/03/10/onlive-coming-to-a-screen-near-you/