Here's our report FWIW:
I received the Darblet from AV Science on Tuesday, and hooked it up between the Denon 4311 and our current 42" Panny G15 with HDMI v1.4 all the way through. I have a 3' cable between the 4311 and the Darbee (a low end $35 Audioquest because that's all I could find quickly at a local Best Buy that was 'high speed' and not priced higher), and simply switched the existing 20 ft. cable we had from the 4311's HDMI out to the Darblet's out.
So far, except for the handshake between source switching taking a few seconds longer than it did before - for both TiVo and BluRay sources, there's about a five second delay rather than two - I'm not noticing any ill effects, green screens, sparkles at the moment. I'll probably try to swap a Blue Jeans Cable 6' cable or 10' cable for the 3' when I've a chance to see if the slightly longer cable run helps, since the Darblet's currently positoned in a less than solid place thanks to our evil small white dog anyway.
As to content: for SD sources, I tested a couple of old DVDs from the 1990's and one of Lisa's compressed to hell shows from E!. I'm getting the most noticable improvement for detail at either Game or POP at about 60 to 65% minimum than on HD at that level or lower, notably on the clarity of background vs. up-front objects. Not so much a "veil' being removed as the sense of solidness that wasn't there before for, say, Tom Cruise or noticing the way that a singer's eyes were moving on a concert DVD, or you could notice the hair on a guitarists arms when he was strumming.
For BluRay (BDP-93), I tried the possibly problematic Hunger Games. I'd started with HD=50%, and found that I didn't get much of any change from 0% until I took HD up to 65% or 70%, yet so far I think HD does 'better' than Game or POP (I saw almost no difference between the three at 65%, so I went with HD as the 'do no harm' option). By change, I mean a more '3D' feel for Katniss running through the forest, or the 'talk show' interview with Cesare Flickerman putting the two actors more up front. Ramping it up any more brought out a little too much detail for vivid colors, particularly the suit that Woody Harrelson's character wore, and created a cadaver-like lividness to Donald Sutherland's President Snow, as well as some smearing of the background.
I need to spend more time with it, particularly in darker home lighting conditions at night, as well as high definition TV content, but right now I'd say improvements are subtle, and more noticeable on A/B of the same scene repeatedly than an "oh wow" effect. But so far, I noticed more improvement in fine-tuning contast, sharpness, and color by running the Spears & Munsil BluRay and tweaking the custom G15 settings from AVS than from the Darbee. However, time will tell if the improvement in presentation is worth the $269 or the minor annoyance of longer HDMI handshakes.
I also wonder if there's a correlation between screen size and settings, with larger screen sizes correlating with less % needed? That would seem to go along with HD=40% and projectors with 70"+ screens.
Edited by sdrucker - 9/27/12 at 2:16pm