the only thing i find with plasma and gaming is over a period of time you might get 'burning' this is where the image from a game for example is burned on to the screen when the console is switched off and is still visible when your watching your regular tv for a period of time. Not too sure if it is common with the newer plasmas but my mates suffered from it. So generally i think LCD is better for gaming and Plasma for movies, but thats just personal opinion and experience.
Utter tosh - Screen Burn and Image retention are two different things.
Screen Burn is when an image is burnt onto the screen permanently causing damage and can't be removed, with modern plasmas this has all but been eliminated.
Image retention is when fixed images on the screen remain for a short while after changing to a different channel (things such as channel logos, HUDs on games etc) - it will dissapear after 10 minutes of watching a moving image.
If you could up your budget I would go for a Pioneer Kuro (9G), unmatched black levels and motion handling capabilites - Panasonic Plasmas are good, but fit a particular budgets and are a definite level below the Kuros.
If you are to consider LCDs I would only go for LED backlight not CCFL backlit screens, which offer a better contrast ration (not a scratch on the Kuros though), but be prepared for motion smearing and color bleed as well as less natural, vivid images.
Read reveiws, and sign up to
www.avforums.com, plenty of experts and users on there who will be able to advise further.
HTH
Anthony