Double-edged sword. With HD, you see more details, like, the writing on a errant scrap of paper on a table in a scene. Also, with HD, you see more details like the wrinkles on the face of EVERY cast member of Law & Order. I mean, even the hot chick.

Over the air HD is impressive, but, reception may leave a lot to be desired. When it is a good, strong signal, over the air HD looks a lot better than Comcast cable in my area (Atlanta, GA).

Tip #1: Make sure you can get an HD source before buying and HD set. WWW.ANTENNAWEB.ORG will tell you if you can get HD over the air, the best way it's free.
#2 Make sure your TV has an ATSC tuner otherwise you will need a seperate set top box.
#3 If not #1 & #2 then make sure that you sat/cable provide can supply the national networks if you are not in than major network locations your going to still be watching regular TV.
#4 Flat screen LCD is best 42" and under. Plasma is best >42". DLP/ Projection LCD is expensive because of the bulbs and shorter lift span.
#5 Check out Consumer Reports for Match if you are going to spend any major cash. I have an OLEVIA 537H - 37" LCD HD integrated Flat panel OLEVIA 537H that I'm happy with and its alot cheaper than a Sony.

I just made the jump to HD this week. Got a 42" Plasma with 720p, and signed up for the HD package from my local cable company. I was pretty daunted when I started this journey, but it doesn't take long to get up to speed, and I must say, I'm thrilled with the results. The Super Bowl looked absolutely stunning in HD.

HD is fantastic. It can't make a terrible show better, but it makes the good shows that much more enjoyable.

All that technical stuff about 720p, 1080i, 1080p, DLP, LCD, D-ILA and so on can be confusing and off-putting for people who don't care about the technical side of things like I do, but the link in the post is a great place to get started. Also, www.avsforum.com is a forum of home theater enthusiasts that are happy to answer anything from the most basic questions to the most advanced.