In-walls/ceilings are without a doubt the most aesthetically pleasing. Since sound QUALITY actually matters, and I'm on a budget, floorstanding speakers are the way to go in my primary listening/viewing area.
But, I think in my next home, the big speakers will be moved to some sort of dedicated theater, and the family room will get hooked up with good in-wall/ceiling speakers. It just makes a lot of sense to get the speakers off the floor and open the room up some.
Gotta say though - I almost went with 'other' and picked on-wall speakers. Wall mounted speakers maintain a pretty good look and should give more performance than in-wall designs for less money.