The Content
I'm sure we've all seen plenty of 1080i content on 1080i capable Rear Projection CRTs or 720p programming on current fixed-pixel rear projectors. We've also all seen what DVD (480i or 480p) looks like on them, as well as lesser quality digital and analog content at 480i. Some of us have even seen DVD upscaled to 720p for the fixed-pixel displays or videogames output to those TV at native resolution. Matching native resolution with the input signal resolution gives a pretty good picture, but upscaling analog cable to 1080i or 720p scan rates doesn't compare to actual HD content because it doesn't carry the picture information needed to have a better picture quality. Upscaling DVD to 1080p for the new Sharp LCD that was mentioned earlier will probably look good, but what's the point of spending the extra money for a 1080p model when the 1080i will show the same information?
If the TV is used for computer use than you will take advantage of the higher resolution. But the thing won't make DVD look way better than on a 1080i or 720p set, other than the advantages of progressive scan over interlaced (when done right). IMO, the content is the key in this decision. 1080p really needs 1080p-filmed material to take full advantage. The use of the TV as a computer monitor classifies as having the content, but the 'home theater' application would not be take full advantage of the TV until there is true 1080p content. We don't even have HD on DVD yet, and very little with D-VHS.
djoxygen is right: it's your call. If you'll use the TV more for computer application then a 1080p monitor could be be justified. For strictly HT use, I would say forget about it for now, except to those people who want the smoothest picture and cost is no object.