Our television watching is divided into two. The bulk is unwinding after a hard day at work, in our loft (previously in our living room). This is television watching where watching television watching is the main point of what we're doing. In this mode, as a rule, we
only watch HD. There have exceptions in the past, such as The Wire, but generally, if the show isn't in HD, or we cannot get it in HD, we pass on it.
We also watch television in the kitchen, sometimes, when cooking dinner and when eating dinner. This is often "television in the background" watching. Almost none of it is HD: This Old House, Sell This House, some travel shows, and some cooking shows. It's about 10% overall.
I'd like to have This Old House in HD, but beyond that, I don't think anything more than what we already have will make a difference to us in terms of HD. Travel shows are great in HD, but when we had a few (back when INHD was still available) it got old quick. Many of the cooking shows we watch now, in the kitchen, not-in-HD are available to us up in the loft in HD, but no big deal, for us.
We recently got FX HD added, and I thought that would be the last HD channel they could add that we'd care about, but it turned out that it wasn't even worth the wait. The only show I really wanted in HD was The Shield, and it turned out that even with the HD channel The Shield itself wasn't in HD. I suppose that FX will have more shows now that The Shield is gone, and they probably will be in HD, and so perhaps that will be appreciated. We'll see.
We currently don't get Lifetime in HD, but there's been only one show we've ever watched on Lifetime (some Canadian paranormal drama, with a partially blind female PI as the lead... I don't remember the name of the show). I suppose that would have been better in HD. (If it was just up to me, I might have stopped watching it before it was cancelled because it wasn't really good enough to watch non-in-HD, but we kept it because my wife liked it enough.)
We used to watch BBC America but they wanted $12 extra per month for it, so we dropped it. That $12 a month included some other channels we'd have watched occasionally (Science Channel,
National Geographic) so I think if BBC America was in HD,
and the shows on it were HD, we'd keep it. However, even if BBC America does go HD in 2009, I think it will be a year or so before even half of their programming is HD. Even then, I still don't think those three channels are really worth $12 per month.
BTW: For folks wondering which channels are available (somewhere) in HD, and what programming is available in HD, here's a full list:
http://www.avsforum.com/avs-vb/showthread.php?t=164671