I've heard some opinions that the smallest TV which can show you the difference between 720 and 1080 is 32" (that's the reason why they don't implement this feature in smaller displays) but it's really difficult. I use 23" Samsung LE23R81W and I'm very pleased with it. If you sit close enough (1,5 m) size isn't a problem. I really don't feel it's too small.

Exactly I have no problem either knowing the screen is small. When its big you can see the difference, but when its smaller you can't. Thats why 720p is what I'm getting cause its affordedable now and not only that 1080p is best to be viewed on bigger screens and I dont have the money and the bigger screen is not necessary for me to have.

You might want to do some research on some place like AVSforum. This topic was discussed to death on this forum (as in many others) and had a link to a fairly informative thread elsewhere. For movies, in my understanding, 1080i and 1080p are irrelevant as the way the final image is constructed ends up producing the same result. I'm no technical guru so please don't take my word for it but the people on here clearly don't know what they are talking about -- such as the one above. Currently all broadcast TV is 720P/1080i. There isn't a live broadcast that I'm aware of, anywhere, that is 1080P native and the likelihood, due to the sheer data invovled is that 1080P broadcast won't be happening any time soon.

Movies are all 1080P/24FPS. Here's where it gets dicey and my understanding breaks down... On a 1080P display, it is capable of displaying its full resolution 60FPS while an interlaced image would be half that or 30 frames per second. Since the movies are only 24FPS, the final image integration process (de-interlacing?) that happens by the time the image is displayed results in a final image that is no different on the 1080P vs. the 1080i display. Again, this is from my limited technical understand and I highly encourage you to research it on your own.

Where you would lose capability is in any source that can display native 1080P 60FPS. The only think I know of at this point that will do that is the 360, PS3, and computer video cards. You would have to settle for 720P output on these devices instead. I think I read somewhere about 720P vs. 1080i vs. 1080p being an issue with some PS3 titles based on lack of a certain scaling chip in the PS3 hardware but, again, research it.

I have a 360, working on a PS3, a Wii, a PS2 and digital satellite. I'm going to buy a 720P set this fall -- most likely a Vizio VX42L series because of the features and cost. I'm not willing to pay for something I will rarely use, but that's just me. Good luck in your search and please, research this until you know what you are talking about before you buy. There are way too many fanboys pushing their favorite and the 1080P vs. 1080i argument is raging. (In part because the low cost HD-DVD players are "1080i" and the Blu-ray are "1080P")

*Edit* -- I've just re-read this entire post and I can't emphasize enough that almost all the information you are reading is just plain wrong. Just because a TV can display 1080P 60FPS doesn't mean you are seeing 1080P FPS. It all comes down to the source. Many who "see the difference" when comparing the two sets are getting the placebo effect...

Here you go.... all you need to know. Get the 720P and move on with your life.

http://blog.hometheatermag.com/geoffreymorrison/0807061080iv1080p/

That tells it like it is. Let me take a quote from it for you:

"When it comes to movies (as in HD DVD and Blu-ray) there will be no visible difference between the 1080i signal and the 1080p signal, as long as your TV correctly de-interlaces 1080i. So even if you could input 1080p, you wouldn't see a difference (because there is none)."

1080p is only really useful on smaller sets if you intend to use them as a computer moniter relativly frequently.

The difference between 480P and 720P is HUGE.  The difference between 720P and 1080P, not so much.  It took me awhile to notice any difference.  I have a 62" 1080P Samsung my friend hooked up his PS3 using HDMI and we could see a slight difference when watching bluray movies compared to his 720P TV.  When playing Motorstorm and VF5, we couldn't see a difference at all.   In fact, he made up his mind that he is happy with 720P and won't be upgrading. 

Yes, if you're doing gaming/TV watching and need a screen less than 40in, go with the 720p and you'll have a pile of savings for more cool games. I'm getting a 1080p screen myself, but that's only because I'll be using it as a computer monitor as well as for gaming, so I need the extra resolution.

For the most part the information being presented in this thread is completely, utterly bogus and poorly informed.  720p is a simple comparison to a width resolution of 720.  1080p is 1080 width.  Due the math, you are talking about a similar comparison of 1024x768 monitor resolution and a 720x540 (making this up) resolution. 

An HDTV is a component device of a home entertainment system.  Will some people notice their optical audio, 5.1 sound on a VHS player?  No.  Infact, probably not at all.  If you don't use it, sure, you won't notice it.  If you are displaying a 1080p media, such as a any signal that is accurately sent in this fashion (not upscaled or downscaled) you will notice a difference period.

The upscaling or downscaling technology is also a HUGE factor in appearance.   I have a DLP projector and the correction on odd resolutions is unbelievable.  Instead of dropping pixels it conforms nearby pixels and very clearly downscales the image.  Most LCD displays, older ones at least, will drop pixels in downscaling a signal.  If you have the right technology downscaling, the image loss can actually work very well.

Interlaced signals and Progressive signals are different.  Some will notice the difference, some will not.  Most probably will.  Progressive -usually- shows a still image better, while interlaced probably shows moving images better.

Although the resolution debate is the kicker.  It's like comparing 7 mph to 10 mph.  You should notice.  The question is what are you needing it for?  Just make sure your downscaling is accurate and presents a good picture.

As has been touched by some other posters, real resolution isn't in the number of pixels total, but in pixels per square inch, and then is dependant on the limit the human eye can decern, and how far away from the TV you are sitting.

So for smaller TVs, you probably won't see a huge difference, but for larger TVs it will be somewhat noticable. If you have a huge tv (LG 102") you will probably see a fair difference, but even then, 1080 probably will look blocky up close ;)

If Gigantic TVs become the standard, don't be suprised if you see "Ultra Super HD" arguments brew over 1400 vs 1920 vs etc, etc, etc.

They mean on a 1080p tv.  1080p tvs deinterlace a 1080i signal and display it in full 1080p.  However, if you only have a 720p/1080i TV, it will display in 1080i at max.