Remember.."Better" is a subjective term.
To me, the improvement claims being layed upon 1080p is 75% hogwash and 25% visual improvement. The move from 1080i to 1080p is an incremental step, just like the move from 720p to 1080p is incremental. There may be a million more pixels available, but to the end user the difference will be a slight to moderate improvement. The quality of the display will also come into play here.
Videogames that are internally rendered at 1080p resolution should look sharper than those rendered at 720p. Movies and TV that are created at 1080p (BD, HD-DVD) may or may not look any better at 1080p over 720p.....that depends on the encoding type done, how the HD master was created, the quality of the print used for the master, how much detail is obscured by video noise due to the conversion process and a whole bunch of other factors that I can't talk to....suffice to say, if you're using a projector...the bump to 1080p over 720p should be "more noticible" than someone using a smaller display, say 60" or less.
I have a 1080p set, a 720p projector and a 1080i set. HD looks "about the same" on all three devices. HDDVD on the 1080p set looks good, but it looks basically as good on the 720p projector which is throwing a much bigger image. It alsolooks just as good at 1080i on my RPTV set.
The real area where 1080p has the potential to show marked improvement will again be with videogames.....because everything in a videogame is in focus all the time, unlike a movie or tv show which uses a lens that has a depth of field where distant objects are out of focus, in videogames (unless deliberately designed this way) everything is always in razor sharp focus no matter how far away the object being rendered "is".
But again.....how much that MATTERS is another story too.
The poster above hit the nail on the head: Technology, in particular HD formats, are in a serious case of Diminishing Returns.
In 3 or 4 years Sony or Pioneer or Panasonic will start trying to sell us "Double HD!" sets....its all about convincing you to buy something new.