Found it to be an absolute flawless experience in the latest carnation.
My PC's an i7 4770K/R9 290.
Done Streaming to my i5 Ultrabook at 1080p over Wifi. I was in fact playing Lost Planet 2 the other day multiplayer with a friend, I was playing via Steam Streaming on my Ultrabook, it was flawless.
I've also played Dirt 3 flawlessly on an old C-50 powered Windows 8 tablet, but at 720p.
There needs to be more bandwidth control, lost planet 2 was pegged at Steam's maximum they've put on unlimited ; 100mbps

but it's either that or limit it to 30mbps.
Need to be 40/50/60/70/80/90 intervals tbh, I'd probably bash it on 50mbps.
As long as you've got the PC grunt (You may need to lower settings to be perfectly honest depending on your machine) and you've got the network and decoding power on the client, it's flawless.
I can't think of any game it's struggled to run, I've done Alan Wake/Rome Total War 2, Dirt, Witcher 1, Witcher 2 etc.
One problem is they NEED an Android client and a Windows RT client, that'd be killer!
I've recently upgraded my monitor to a 21:9 2560x1080, and was VERY impressed that streaming to the Ultrabook at that res would maintain a 21:9 aspect ratio (So, 1920x800 something) and it looked VERY sharp, sure, black bars, but we're on an 11.6" 1080p panel here, everything's just crisp and clear.
I've found laying in bed gaming to be very comfortable to be honest, although I get the distinct impression that I'm only one of few that's heavily used the in home streaming.