I haven't tried it, but I'm pretty sure Win->Win streaming works.
I finally got steamos installed on the weekend and it's very much a beta product. Most of the stuff that needs polish is related to the operating system specifically, I had issues with trying to use some basic system options such as switching users and it refused to save my HDMI port as the default audio output. It also refused to login and load up steam in big picture mode directly, no matter what it drops me to the desktop and I have to load steam directly. I tried all of the various desktop options (Gnome, Gnome Classic, Default X Session, and steamos) and it was the same thing for all of them. The install had a bunch of issues where it would randomly fail, I tried a few USB keys to rule those out but I ended up having to take out my 6970 to get it to install.
Steam itself seems fine, the only thing I found pretty terrible to use was the actual setup of my 360 controller. It makes you configure all the buttons one at a time via the interface but if you mess up for any reason you have to abandon the entire setup. Since it's making you configure the axis directions, as well as analog stick button clicks it's just ripe to accidentally click something wrong. Without a mouse/keyboard to correct things the controller is effectively useless because you have to abandon all the bindings, which means doing anything on the controller does nothing. Other than issues with the bindings it was pretty straight forward after that, it functioned almost entirely like the Windows version.
Streaming worked pretty well, I tried Batman Arkham Origins for a bit. For whatever reason near the beginning of the game the FPS dropped to something retarded low like 6FPS for awhile, but after that it was at a solid 60 for the rest of the game play. I have an i5-3570 powering the machine/graphics and it seemed more than sufficient for smooth streaming game play. It consumed 15megabits roughly streaming, and the latency seemed fine. Near the end of the session I had an issue with Batman's view always moving to look towards the floor, but the cat was laying on my HTPC controller so it might have been interfering with the game.
Overall it wasn't a terrible initial experience but unless you have some decent linux skills it might be quite the pain to navigate through and deal with the quirks.