Well, it's all about how far you sit from the TV. If you have a big screen and sit very close to it, 1080p is the way to go, but after a distance(let's call it X), your eye won't be able to make out the differece between 1080p and 720p anymore.
There isn't much material available in 1080p yet, except for movies that is, so if you don't plan on buying a lot of HD-DVDs or Bluray discs, you won't benefit from the extra pixels.
1080p won't be supported for broadcast in a while, as it requires(dare I say it?) almost too much bandwidth. So we're going to be *stuck* with 720p or 1080i signals for quite some time yet.
A 1080p capable TV is also more future proof than a 720p one. And 1080i looks pretty awesome on a 1080p TV, and it's better suited for a HTPC.
So what I think you should do is measure the distance between the place where you'd place the TV, and where you'll be sitting.
Then go to a store and look at both 720p and 1080p material to see if you can spot the difference(approx. at the distance you measured earlier). If not, then you can save a buck or two by buying a 720p TV, otherwise you'd be better off with a 1080p TV.
Plasmas have a much better pic than LCDs imho, that's only quality ones though, and you'd have to pay a very hefty price for a 1080p Pioneer or Panasonic.
So just get an LCD, it's not worth the hassle with plasmas(burn-in, colours fading after time etc.) even though they might have a better picture quality.
Hope this answered your questions!