I have a friend who was using ceiling mounted surround speakers but recently took them out in favor of towers. His speakers are all from the Klipsch reference line.
I brought a pair of bookshelf B&W speakers (602 s3's) over to his place and we switched back and forth between the ceiling speakers and the 602s. The ceiling speakers just didn't have the response in the midrange and the lower frequencies - he described the ceiling speakers as sounding "thin" compared to the 602s, which I think was a good descriptor. Like I said, he ended up buying a pair of RF-62s (which he put in the front), and he moved his RF-3s to the back for surrounds.
My friend likes to listen to his music in 5 channel stereo mode, and he was looking for a more even tonal balance from all the speakers. I can see why he wasn't completely happy with the ceiling speakers. They are definitely a compromise between sound and decor.
I guess the point is that you may have to sacrifice some sound quality if your setup is on par with my friend's setup. That is what I have found with my extremely limited dealings with ceiling surround speakers.