yep. There's been a recent thread which addressed the subject in depth, entitled something to the effect of "Are you still happy with your ED panels?" I suggest you find it, and it could be quite instructive for you. Given how the forum has been split into subcategories recently, I'm not sure if you'll find it in this forum, or the Plasma specific forum. In either case, I think it should appear within the first few pages of either forum. Prices differences between 42" ED & HD are typically within a couple hundred of eachother these days, when they used to be several hundred, so it should be noted that for such little difference, many feel it's best to go for the HD nowadays. Good cases can be made for either decision, and you probably can't go wrong either way.
Actually, let me amend that by saying at 7-8ft, you reeeally should visit a few stores, find and ED & HD panel (often side-by-side), tape measure the difference to match your seating arrangement, and assuming they have a half way decent HD feed going, look at both and see how much difference you can see. Preferrably at a smaller botique or higher end a/v store, as they are more likely to have a better setup. You start to see what is called the "screen door effect (SDE)" , a grid like pattern in the panel, the closer you inch towards both the ED and HD panels. You'll notice it first from the ED panel before you would from the HD, but it's there for both. These are basically gaps between the pixels. Less dense pixel structure means more "screen door" when viewing up close, which varies depending on the quality of your vision.
As far as 42" Panny pricing, around Thanksgiving, some popular merchants had one day $1k prices. I can elaborate no further, as we are forbidden from discussing prices on the forum in too much detail. But sale prices like this will likely become more common over the course of the next several weeks. I've looked through the craigslist in my Chicago area on occasion, and I've never been inspired to pursue it further, as prices were rarely all that impressive (I've found), and unless it's a outrageously good deal, I wouldn't risk it.