I know it can happen and while the technology is improved it is still possible to get image retention (IR) that fades in some amount of time. The burn in is such that it sticks around for days (that's still called IR!) and long term use can result in the effect that sticks around for what may be forever. The pixel rotation helps smooth that line in the 4x3 viewing.
You didn't tell much about the old CRT. Or why you didn't consider a set of the same number of inches or even LCD.
My mother's CRT finally gave up the ghost. She went out without me and bought a Samsung PN51E550 plasma that is to be delivered tomorrow.
I've never had a plasma but I'm concerned about IR or burn in. I went to an official Samsung site and read some FAQs. They are very straight forward about the fact that burn in IS NOT covered by the warranty.
Now I understand with the new pixel moving tech that for the most part it is no longer and issue but here's the deal, my 76 year old mother watches a lot of the old classic movies which I'm pretty sure are mostly broadcast in 4:3. The FAQ that mentioned not covering burn in, also warned against watching 4:3 content with the black side bars, for any more than 5% of your viewing time. Well for my mom, that would probably be more like 50%.
So in order to avoid ruining a $900.00 TV with no warranty against burn in, I assume she would need to use one of the picture size options that stretches or zooms the image.
If you are experienced with plasma TVs, please tell me about any burn in problems you may or may not have had and even more importanly, please tell me if any of the picture size options work well for you as apposed to looking obviously distorted or cut off.