Well I said I'd report back after I got it set up so here I am.
It works perfectly with Windows MCE 2005 and my ATI Theater 650 tuner. It has the codes for MCE already in its database so all you have to do is go through the wizard and tell it what devices you have and how they're connected and it's done. I have a MCE PC, LCD HDTV, satellite STB, and air conditioned set up on it and it all works flawlessly. Even my Samsung air conditioner had codes already in the database, I just had to program the 'energy saver' button into the remote but it was really easy. The one thing I was worried about was, I had read that the remote would be state-unaware, meaning it wouldn't have any way of knowing if your MCE PC was already on and might toggle it off if you started an activity that required the PC. In fact, it has codes for 'on' and 'off' and just uses the 'on' code when you start an activity, so if you already had your PC on it owuldn't matter. Ingenius.
I have to wait and see if it will conflict with my MCE laptop in the same room, it's out at BB for repair right now.