I am a die-hard pc fps gamer. I loved playing Call of Duty 4 on my pc machine until my computer totally crashed. So I bought a ps3, along with cod4. I was so disappointed playing it with the ps3 controller. I am so used to a mouse and keyboard. So I took the plunge and bought the xfps adapter.
First off, it works great. It comes REALLY close to replicating the feel of an fps game on a pc. It takes some time to really dial in the x/y sensitivity, but once you find the sweet spot, it really works great. I'm using my razer copperhead mouse and a logitech keyboard. There's really nothing like playing cod4 on my 42" plasma with my mouse and keyboard hooked up to my ps3. The xfps does a really great job.
Now for some of the little drawbacks. For some reason after I've unhooked the controller, it won't remember my "back" button. I've mapped "s" to be my "back" control on my keyboard, and I have to remap it every time I start a new session. Once it's plugged in and mapped, I can go as long as I want. But once it's unplugged, for some reason it doesn't remember it, so I have to remap it. Not sure why, maybe I just got a funky unit.
They should have added in a 3rd usb port for easier mapping. As is, when you want to map your controller to your keyboard/mouse, there's only 2 usb ports on the xfps, one of which is taken up by the ps3 controller during mapping. So you basically have to plug in the ps3 controller to one usb port on the xfps, plug your keyboard into the other usb port to map your keyboard, then unplug it, attach the mouse, and then map the mouse. It's just more of an inconvenience than anything else.
The other thing is that the extra side thumb-buttons on my mouse can't be mapped. I didn't really expect that it would be able to map those buttons, but if they could be mapped, it would have given me the complete pc fps experience.
So I have a few qualms with the unit, but it's mostly to do with the mapping of the controls. As for the game play, honestly, I have no complaints. It's not perfect, but it's really, really close. If you're a pc gamer and you're used to a keyboard and mouse for fps', this is a must buy. It is well worth the price tag, especially with a game like cod4.