Audiotomb you brought up another excellent point which is how good is the scaler in the TV sets. Ok I Over generalized for most people (I do prefer a big presentation) but what makes 1080p look good is how close you view it... if you are seeing artifacts on a 1080i then the scaler in the lower end set is to blame or the source. 1080p tv will in general have a better scaler.
I highly highly recommend checking scaler quality or going external (Lumagen, DVDO, etc.) as this was the most amazing upgrade for my system. on my 103" I don't see artifacts with my 720p projector and that's impressive.. if I were to hook my cable box directly up to my PJ it would be block city and tons of panning motion artifacts even on HDTV. My old 720p DLP optoma projector had an excellent Scaler, my current Sanyo Z4 LCD has an awful scaler.
So if you can watch the set you want to buy with an OTA signal, bring a DVD player or have them hook up a dvd you are familiar with and look for jaggies, blurring in the backgrounds, etc... artifacts like these are annoying.