So...I bit the bullet and ordered the Down and Out Mount from dynamicmounting.com too. I have a 50" Panasonic Plasma TV. For a few months after we moved in, it sat on the floor in front of the fireplace while I searched for a solution. I now have it mounted above the mantle. The TV itself weighs 75 lbs. The mantle is 9" deep.
The studs on my wall were not conveniently aligned, so I mounted a couple of 2x2's to the wall, then installed the mount on them. I painted them the same color as the wall, so they are fairly unobtrusive when the TV is "deployed." Because I have the 2x2s on the wall, I get a little more vertical movement than mounting the unit directly to the wall, but I get about 29" of vertical movement.
Shipping on the mount was $39.29, so not too expensive, it is a fairly heavy piece of equipment to ship through the mail. Shipping was to Goldsboro, NC 27530
You can adjust the TV to be totally vertical if you like, I have mine slightly angled down in the "Up" position and vertical in the "Down" position.
The TV "locks" in the up position and pulls away from the wall when you are moving it. So if you wanted it in a cabinet up high, it would most likely work as the TV moves Out and Down simultaneously.
You can adjust how much pressure it takes to move the TV. I adjusted mine so that the weight of the TV will not quite move it down to the full down position, I have to push it down to full down. It takes about 20 lbs of lifting pressure to move it back to the "Up" position as well. You could adjust it to provide more or less lift, this setting works for me and my wife and strikes a good balance.
I'm happy to answer any questions.