I've been using it since early April. Bought the Premium service. I have picky eyes so the HD quality seems worth the extra bucks to me. Lags a little now and then, mostly w/the fast-pans of camera, but nothing disturbing. Usually it's fine.
What I like most is I can hook the PC up to the 50" TV and it still looks pretty damn good. Not super-HD quality, but better than some of the crappier HD signal broadcasts cable likes to give you at times.
The NexDef seems to have problems and sometimes isn't working, and so far it's cut out completely for a few hours a couple times but eh...I figure it's still better than not seeing the games at all (since I live in California).