Ok, well I have done enough listening with them to comment properly...
First thing, these 'phones do not look or "feel" like they cost $79...I don't think you would confuse them with $1,000+ 'phones, but I would never guess they were so affordable just by holding them.
Second thing, they are light and very comfortable. I tend to avoid headphones unless necessary as most don't sit well on my head (I have a big head I guess). Most are ok for a while but then the "vice" effect takes place and I have to take them off. Well, the UF-30 don't cause that problem at all. No "squeeze" going on, and they are light enough that I almost don't realize they are even there. I tend to prefer "around the ear" as opposed to "on the ear" but the pads on these are soft enough that it doesn't bother me.
Now, sound quality...tonality wise, I'd put them very close to the NE-8's, and by extension, the Icon desktop setup. Clean, clear, very open sounding. I am not familiar with S-Logic or Ultrasone's products but one thing I noticed right away was the height of the soundstage...on some recordings the sound almost appeared to be above my head. It didn't come across as gimmicky, or in a "fake surround" kind of way, just felt very "big". Nice width to the soundstage too, of course, but I suppose I was expecting that a bit more.
I don't want to give the impression that you need to sell your TOTL Stax or Sennheisers, because they are different beasts altogether, offering things the UF-30 doesn't do (more bass for one). But then again even if you have those giants I think the UF-30 make a perfect 2nd (or 3rd, or 4th, etc) set, as they are very portable (beyond being light they also fold up, and I believe the full production model will come with a carrying case), and offer a sound quality that is honest to the source.
Finally, I think its great that NuForce offers these in so many different colors...while I can't imagine going with something other than black/white, I know other people that want something more "unique and noticeable", so now everybody can be happy.