I have a SHIELD tablet I bought at release, and I use both the PC to tablet Gamestream and the online GRID streaming (nVidia sure like their caps).
Both work surprisingly well. I'll sometimes play XCOM on my tablet at work during lunch break and at first co-workers were asking how I got that to run on Android. My upload at home is only 10Mbps, but it's apparently more than enough for decent quality at 720p so I can play any Steam game at work.
For GRID, I've tested a few games, but the only game I played through the end was Darksiders 2. I was surprised that you can't really feel the lag, even for action titles. My main gripe with the service is the game selection. I'm a strategy / rpg junkie, but the only quality game that I really wanted to play on GRID is Witcher 2. However, I've already completed it 3 times on PC so it's not like I wanted to play it again. I've tested it though, and it works well.
All in all, I think the technology and infrastructure is getting ready for game streaming. I suspect that nVidia has a potential hit on their hands.