Despite the claim of M$ to create the first YouTube for games, this kind of sites already appeared.
Example : http://www.threesixbox.com
(there are a few others, but I dislike them, their games don't work well and I needed to patch them)
There are also open source libraries creators giving their work for free:
Example : http://www.xgamelibrary.com
I guess M$ it taking its time to make a nice site, full of highly profitable ads... (Takes time!)
Also check that smart guy willing to sell the yougame.com domain he quickly reserved...