I have the 880 and love it for the functionality. The web setup is very easy to use and makes setting up activities a snap. It controls all of my components without a problem, TV, receiver, cable box, and dvd player. It comes with a rechargeable battery and it's own recharging station, which is a nice feature. I don't have an xbox, so I don't know how it would work with one.
The biggest compliment I can give this remote is that my wife can now switch from watching tv to watching a dvd with one button, and without the need to call me on my cell phone if I'm not home. I was in Vegas once with the guys and got a call at a craps table that the dog jumped on the romte and now there is just a black screen... no more calls like that with the harmony.
Ok, now on to the cons... I don't like they way it feels, it's very light and it's almost slippery. I had a Home TheaterMaster before the logitech and it had a rubber-like coating that made it stick in your hand. The buttons on the logitech are very close together and I somtimes have trouble hitting only one with my thumb. Although I mentioned the rechargeable battey as something I like, I am a bit worried about the availability/cost of a replacement battery when mine dies.
All-in-all it's probably the best home theater remote I've used.