I see two problems with the wal units: wires, and accessories.
Yeah the wall untils look cool in the commercials, but they don't have any wires in the commercials. I suppose if you're willing to tear into your wall and do some creative rewiring you can still achieve that look but that's a lot of work.
And the modern TV is not a standalone unit, at minimum you're going to have some sort of cable/ sattelite receiver it plugs into and a DVD player, and possibly other (probably other stuff if you're going in for a high end TV, what good is the uber TV without surround sound). Where all this stuff supposed to go when your TV is sitting on a wall.
Flat screen TVs are cool, but I just don't think the wall mount has that big a market, between the cables and the extra hardware you're looking at 2 to 3 feet worth of stuff that's gotta go somewhere, which means some sort of entertainment unit, which is a fine place to put your TV.
Just make it wireless....