Plasmas are usually considered the technology that has the shortest life span, but to put things into perspective:
I think most modern plasmas are rated about 60,000 hours of watching ....That's almost 7 years of continuous watching!
(LCD is ~70,000-80,000hrs)
I highly doubt you'll use your TV 24/7, so, even at 12hrs per day, you're up to almost 14 years of life.
In other words, you have better things to worry about
