I put some on my 945 about 4 months ago. I'm happy with them so far, I have noticed an increase in braking performance, but to be fair I also put new rotors & brake lines all around and new semi-metallic PBR pads on the rear as well as replaced a frozen caliper in the rear at the same time.
With that being said, one thing that is very different is almost no brake dust build-up on the wheels. To me this is a benefit, I like a clean car.
Another consideration is that ceramic pads are said to wear your rotors more quickly. My research lead me to the conclusion that fancy slotted, drilled or otherwise over-the-top types of rotors won't do much for you in normal daily driving, and that many of my fellow brickboarders found the standard Brembo rotors to be the preferred replacement unit with a very reasonable price. I figured that even if my rotors only last as long as one set of pads, at $60-70 for a new set that would be O.K. with me.