The answer, as usual: it depends. First of all, keep in mind that no one broadcasts in 1080p, so if you're not watching blu ray or playing games in 1080p, the whole thing is moot. Second, whether you would be able to tell the difference very much depends on the distance from the screen to you. I have a 50" 720p plasma, because there would be no point in me getting a 1080p - I sit 15' feet away.
Here you go: