Seriously, I am moving right now and looking for a wall mount for my 50 inch plasma, which is probably 150lb. Wall mounts that can handle plasma screens are not as common as they used to be. For wall-mounting, it's almost worth buying a new LCD to save money on the mount.
I have never wall mounted my LCD TV's. I guess that would be a good option, I just never need. I think I would want a model with a swing arm that would allow me to angle it off the wall a bit to avoid reflections. We have a couple of those at work that I might look at with my next purchase.
As far as is it worth it? Some mounts can get pretty expensive, but they are usually less than the cost of a new TV. Maybe make sure the mount can handle a newer LCD TV as well as your plasma in case you make a change in the future.