I'm quite techie and I'm now on my 2nd LCD HDTV (a 40" 720p Samsung). However, I don't have a Blu-ray or HD-DVD player, haven't even considered buying one and don't intend to get one in the near future either. 99% of the time the TV is used to view transmissions from my SD cable box. I'll probably move across to a HD cable box in the next year but even that won't have many HD feeds (I'm too tight to pay the premium!) so, for the foreseeable future I'll be mainly viewing SD transmissions.
I've recently set up a HTPC and have viewed one or two HD feeds through that and there is a noticeable difference to SD. However, for a 40" TV the optimum viewing distance for 720p is apparently around 8 feet. If I sit this distance from my TV and watch an SD broadcast, the image quality is absolutely atrocious, not to mention the fact that I'd have to move the coffee table out of the way then shift my chair into the middle of the room! Therefore, I sit about twice that distance from the TV - SD broadcasts look fine, HD feeds look a bit better and I'm quite happy.
I know that all of my friends who have HDTVs are in a similar position (though a couple have PS3s and have purchased maybe a couple of Blu-ray movies) and, until HD broadcasts become commonplace on terrestrial TV (i.e. free transmissions), I can't really see HD really becoming as important as some in this thread seem to think it already is.