I tried this during the beta, it's really cool, but unfortunately the input lag was noticeable even on medium-paced games. I was running it on 1080p through my gigabit ethernet. They added new options since I tried it, so I'll test it again and report back.
Edit: Input lag is better, but video lag is worse. Even with 720p downscaling on "fast" quality (i.e huge artifacts), streaming a relatively modern UE3 game was too laggy, but indie games worked pretty well. My PC is running a GTX570 and an i7-3770. I'll try again some other time, just in case something else was hogging my CPU/network.