Samsung 52a630, I couldn't move one foot to the left or right without seeing some washout and color fluctuation. (two separate units that both had this issue) it wasn't what I would call a deal breaker, but it was there and it was noticeable. (most noticeable on shadow details as they got better as you go farther off axis) it got worse the farther off angle I went as well.
As for the floating blacks, try out the various dynamic contrast and energy saver modes, some of them dynamically adjust the backlight which causes the black levels to fluctuate. (which is why I hated using game mode on the thing, energy saver set to medium or high was needed to bring screen brightness under control, but it messed with dark scenes too much thanks to it dimming the screen to save power crushing many details in the process) it isn't quite the same as on a Panasonic plasma, but it produces a similar effect in that black levels fluctuate based on content.
Sony sets do this as well, it was originally added in a firmware update to fix the mura problem in the xbr2/3 and has persisted in every Sony LCD released since. They finally have gotten rid of it in their 09 models with a firmware update that seems to have eliminated it.
As for it being different on various Panasonic sets, I can make it behave differently on my Panasonic set simply by adjusting the settings and picture modes, with my current Cinema mode settings, it is rarely noticable and you have to watch for it, on vivid mode it is noticable on most every dark scene I watch, regardless of black bars. I'll be sure to do extensive testing on the 50g10 once I get one to see if it has the problem as well.