Bugger! Can't watch the cricket on the biggest and best display (Panasonic plasma) in the house. Since Sky added the Olympic rings to the bug it has been full brightness with maximum image retention power. Sky, this is a dumb thing to do. There are still many people with plasma displays.
Have owned plasma TV's for years and never had any problems with image burn-in. Most channels (including Sky) have a watermark effect on their bug and there isn't a problem.
Watching a game of rugby for a couple of hours is fine but five days of cricket is a different story.