From what ive heard it takes quite a long time fof continuos game play before your in danger of burning in an image from the Xbox. Plus alot of games now alter their menus and life meters to go lighter just for that reason.
By playing different games and as mentioned before by keeping contrast low. I have never seen a problem but most of the games I play are like Halo with the opaque graphics.
I have a RPTV and have not had any problems with burn in on mine. I have a 4 year old sony and it doesnt have any marks on it from dvd, consoles, etc. You should be fine.