I've had my Panasonic ST30 for a while now. Ran the slides for 100 hours and configured it to D-nice's settings. Have never had any image retention issues. The other day I decided to try Wipeout on PS3 in 3D mode. I don't have the glasses, but just wanted to see how it would look.
The first thing I noticed was that the company logo left a shadow on the screen after the image changed. This was despite only being on the screen for a few seconds. I immediately got freaked out and took it out of 3D mode.
Is this something to be concerned about? It's totally fine in 2D mode.