From what I've read at AVSForum and in other sources the official (or un-official) lifespan of plasmas as stated by some manufacturers is around 20,000 hours (some state more, some state less). In my house the TV set stays on all day long 10-12 hours a day on average, which I admit may not be typical. So, according to my calculations it won't last 5 years in my case.
I don't like watching stretched images, so CNN and other SD channels are always 4:3 on my TV. If the burn-in is no longer an issue with plasmas, I am happy to hear that. This is news to me. I know it is not an issue with LCD.
These were very important considerations in my decision to go with LCD RPTV(GWIII), in addition to the price of course. Sure I will have to replace the bulb in my TV set, but this is not a big deal.
Again, I didn't mean to start a new discussion about Plasma and it's burn-in. I know there are on-going debates on this and a lot of controversy. I am no expert in plasmas, and I am not going to take any side on this. All I am saying, is that if you are considering to purchase a plasma, make sure to research this subject, and make up your mind knowing all pros and cons.