Differences between CRT and flat panel

[Jeffhs]

I have a flat-screen TV, but I have heard and read these sets don't last all that long compared to CRTs. My question is, if I go back to using one of my 19" CRT televisions after the flat set quits, what differences, if any, will I notice in the picture? I realize I won't be seeing HD, even if I use a cable box ahead of the set, but I'm wondering if the picture I do see will be any clearer or sharper than NTSC was. One concern I do have is the letterboxed picture I will likely get on channel 3 (NBC) in Cleveland, which is full HD. Will the black bars above and below the picture eventually damage the CRT? I realize there is no way to eliminate the letterbox effect without an HD cable box ahead of the TV.

Thanks for any and all replies.