I have the 63" Samsung plasma; I do a lot of gaming in general and my experiences pretty much mirror those of chriss2d.
2D>3D conversion doesn't do much for most of the games I've tried. To date I've played Dead Space, Prince of Persia: Forgotten Sands, Bad Company 2 and Forza 3 on the 360 and both Uncharted games on the PS3. After playing around with the various 3D settings and maxxing out the depth setting you do get a subtle sense of depth at times (Forza 3 and Uncharted 2 probably being the games that benefit most of the games I've tried) but it really doesn't change the experience in any meaningful way. As far as movies go, it really depends on the film. The effect works best with movies that have relatively static camera shots or slow pans. For example, Star Treks II, III and VI were all shot this way and have plenty of 3D moments in them, while the 2009 Trek reboot, with its shaky cams, lens flares and fast cuts, does not. The Good, The Bad And The Ugly with its extreme closeups and carefully framed scenery also looks good in 2D>3D.
As to native 3D games, I've played the Motorstorm 3D demo and have the full Wipeout HD and Super Stardust HD games. I also have the Avatar game for the 360. In each case, the 3D effect is very pronounced and the games are still colorful. The Samsung plasmas have a Game Mode that seems to work well and lag hasn't been an issue yet. In terms of ghosting, I've only seen it during some of the closeups in cinemas with the Avatar game; tweaking the brightness, contrast and panel light settings alleviated the ghosting greatly. I never experienced any ghosting with Sony's native 3D games.
In terms of image retention or burn-in, only Avatar has given me a little trouble. After about 1 hour of playing I did see some faint IR when using the TV's anti-burn-in scroll wipe feature to check for afterimages (it wasn't visible during normal viewing). The afterimage quickly faded away but I've decided to put Avatar aside for now until the phosphors in the TV have a chance to age a bit.
Regardless of whether you go with Samsung or Panasonic, it's a plasma TV so you will want to monitor your viewing habits, especially during the break-in period.
On a slightly off-topic not, going forward I wish more developers would give you the option of turning off any static huds or at least allowing you to control their transparency in their games to minimize any IR. After all, how hard could it be. The Motorstorm 3D demo for example used transparent huds during the race and even after repeated races there wasn't a trace of IR.
Xbox Live: XboxPhantom