I just tested out the Steam In-Home Streaming beta and it is working incredibly well!
The first bit of good news is I can finally have two systems with Steam logged in. Once they're paired (which is also made extremely easy though Steam's settings), it's a simple operation. The "Installed" list of games shows you all the games that are installed (on both systems). Any game that is not installed on the system you're using with have a "Stream" button instead of "Play." It's so simple and painless.
The quality of the streaming can also be controlled through the settings. You can leave it to automatically adjust depending on your network capability or you can configure it to your liking e.g. only 1080p/720p/480p, manage network traffic, prioritization, etc.
I've tested it out with all sorts of games and the results are blowing my mind. The latency is really low, so games that are very sensitive still play really well. I've been playing Batman Arkham Origins, Castlevania Lords of Shadow 2 and Mirror of Fate HD (which is awesome if you love Metroidvania btw), and BioShock Infinite. The visual quality is fantastic, streaming at full 1080p, and I didn't experience any input delays. It felt like I was playing it as intended.
I haven't tested if it works with non-Steam games that are dded to the games list though. Hmm, it would be sweet if that works too!