10 Years ago I bought a Toshiba 36" CRT with 800 lines of resolution that upconverts signals using artificial intelligence, or so I remember from Best Buy. ($2000) Anyway, this picture is glorious and everything I watch is like HDTV 720p. I use digital cable, but not the extra HDTV service. DVDs look good, too. Should I upgrade?
HDTV is great. Bigger is better (IMO), depends on how much one wants to spend on a new TV. All broadcast TV will be digital in 2009, so you have some time to make a deceision.
Digital signals are very good, no snow, no ghosting, either you receive the signal or you don't. Fringe area reception will need a larger outdoor antenna if for OTA reception.
(antennaweb.org will show you what OverTheAir TV signals are available in your area.)
I remember seeing someone's Proscan almost 15 years ago. It also upconverted and got rid of the scan lines. The picture was incredible from a regular cable signal. OTOH, I go to some stores and see them try to run a regular signal through some of the new TV's. They look terrible.