a 1080i TV has 1,080 lines of pixels, however only half are used at any one time. a 1080p TV uses all the pixels at the same time, therefore more pixels = better picture if it's connected to a PS3 which can provide FULL HD images... awesome!
however you also need to consider what else you use the TV for since the FULL HD TV's can look fairly average if the originating signal is poor.
not sure what your system is in the UK, however in AUS we hv 5 free to air networks. only one of them broadcasts in 1080i, while 2 broadcast in (approx) 720. That's all about to change as each of the networks brings more channels on line each including HD channels later in the year. based on the above, watching a program on a FULL HD TV ranges from amazing to down right terrible.
our major cable (pay TV) supplier is FOXTEL. around 70 channels in standard definition digital. again, picture quality for these ranges from excellent to awful.
I guess the thing to remember is a FULL HD 1080 TV has the ability to maximise a picture and provide amazing images... watch a newer Blu-Ray movie on your PS3 and you'll see what I mean. Down side of course is these TV's tend to "amplify" any imperfections as well. So if you enjoy watching old episodes of "M*A*S*H" or something like that... the result is not too good.
another interesting note... watching a live broadcast, say the News in 1080... the "hot weather girl with the beautiful eyes" may look a little older as you start to notice every line on her skin! also, movies with average special effects get caught out, for example, watching the movie "Fantastic 4" on Blu-Ray... the "THING's" suit looks very "rubbery". Is it possible there's just too much detail?
this will change as studios spend more on special effects. The big attraction for the studios on all this high def stuff is the movies are so darn big in terms of file size they are impossible for most people to download illegally.
so to answer your question:
Quoting I.D. What kind of specs do you need to look out for with HD tv?
to maximise the "potential" of your PS3 you need a FULL HD 1920 x 1080p television. however there are pros and cons to consider based primarily on what "else" beyond watching Blu-Ray and playing PS3 games you want to do.