I am a (not so) proud owner of the Intel set. Granted, when I purchased it, it was the only wireless option, but anyways... heres my 2 cents
For starters, it (the set of devices - base station, gamepads, keyboard, mouse) does not have native Win2K support. Intel did release unofficial drivers, but some of the functionality is missing and installing is a pain.
The keyboard is decent, although not very comfortable IMO (kinda bulky). The D-pad is just one large button, which makes it difficult to use. Battery life on the keyboard is fine.
The gamepad is my favorite piece of the set. Nice and comfortable to use, and the fact that you can use it as a mouse is convinient.
The mouse sucks. YMMV on the battery life, but mine cant go 3 DAYS without needing a new set. Definitely not worth the $ IMO.
I really only use the wireless stuff to control mediaplayer/winamp and occasionally IM people while I am laying out in another room using TV-out. The gamepad is more than sufficient for controlling the apps and the keyboard is passable. I would NOT use this as my primary set of peripherals.
My brother recently bought the microsoft set for similar purposes. I have not used them, but the design of the devices is identical to the design of their wired devices, which is a good thing IMO.
Hope this helps