It's a fantastic product. I got mine for free for pre-ordering Assassin's Creed: Revelations on the OnLive service (total cost: ~$45 with shipping).

It's tiny!

The OnLive UI is a bit cluttered at the moment. It worked when they launched and had a limited number of games, but with the current number of titles, it's hard to find things. Still totally works.

Boots up incredibly fast. I can get into Saints Row: The Third in about a minute from the console being "off" (it's always in standby mode unless you unplug it. Apparently super low-powered, though, so no worries about electricity waste)

Game selection is ... pretty good. Still early in the life of the service, but it's missing games from EA, Activision, and Bethesda. They seem to have a good relationship with Ubisoft, THQ, and tons of Indie Studios.

Controls wonderfully. Controller is a bit bulky for me, but it performs just as well as an XBOX or PS controller. Wireless, only works with the microconsole, no PC, Tablet, or Mac use. Can hook up a mouse and keyboard to the microconsole, so you can get your RTS on on your TV!

Performs perfectly! As long as your internet is great. Mine hiccups occasionally (has to do with your ping to the nearest OnLive datacenter), so I don't get perfect performance, but that's my problem and not the console's.

Console is always pretty warm. Even when on Standby. Mine makes a very noticeable high frequency tone when it's in standby mode. If I unplug the HDMI cable, though, it stops. NOT GREAT. But I've set mine up so this isn't a problem.

If you pretty much only game at home, OnLive might not be the best choice. But I game primarily away from home (my job doesn't require me to do much more than sit in a seat for 6 hours at a time in front of a crappy pc), so having the MicroConsole at home is wonderful for seamlessly continuing the games I've been playing elsewhere! Definitely check out your internet connection before you order the thing.