flat screen wall mount question

I would like to mount a Samsung UN46B8000 46" that weighs about 35-40 lbs. on one of those wall mounts that tilts, swivels, and extends. My question is, for the people that have similar displays mounted like this, do they wobble around, when repositioning them, or are they smooth and fluid? Or if somebody just touched it (Heaven forbid!) or bumped it, would it shake? I don't know of anyone personally using one of these, so I've never seen one "in use". I think I'd rather just mount it solidly to the wall (with no tilt/swivel/extend properties) than to have it all "wiggly" when moving it.

And do they loosen up over time? I would hate installing one and then have it "fatigue" after a while.
If your moving it anyway whats the big deal if it moves slightly for a second? Its not gonna flap around for 30 seconds lol.
I have 2 of the Omni mounts. We sell them at our store. One has a 42" plasma, the other a 60". They are fantastic. Super smooth, stays where you want it when you move it. Very fluid, and easy to install. The arms are hollow, so you can run the cables through them. If there is a better one out there, I have not seen it. If you want, shoot me an email and I'll send you some pictures.
No worries with a trusted brand like Omni or Sanus...though I cringe at the prices. As long as you use 3 or 3 1/2 in lag screws in the studs that tv "aint goin'" anywhere.