I've spent about a month with the V-Moda Vibe Duo Nero headphones. I am not displeased.
Designed specifically to work with the iPhone, the Vibe Duo Nero are different from the Vibe Duo only by the addition of a control button on the microphone like the one on the stock iPhone earbuds. And while it works, it can be a little bit finicky to use, as the metal button is only slightly raised on the round metal microphone housing, making it occasionally difficult to locate without looking, especially with gloves on. That sounds worse in writing than it is in practice. Certainly don't let that dissuade you from purchasing them.
The iPhone has become my primary music device, which means I no longer have to question whether or not I am going to carry my iPod with me or not. Unfortunately, that meant I had to carry my headphones with me everywhere. My previous on-the-go headphones were the Sennheiser PX100, and while I have nothing but good things to say about their audio quality, they aren't exactly pocketable, especially when you're only wearing jeans.
The Vibe Duo Nero on the other hand slip easily into a pocket. When using the included spring-close leather case, they even remain generally free of tangles.
Sound quality is very good, although few "low-end" in-ear models are going to be able to reproduce sound as well as full-sized headphones. For public transit riders like myself, though, the sound from the Vibe Duo Nero is actually a little bit better than most, simply because the earphones act as earplugs, blocking out outside noise. That's especially good since turning up the volume on my Sennheisers to drown out the subway noise was certainly bad for my ears.
The mid-range tones seem to be the weakest, actually, while bass is fairly round. That's pretty much in line with every other in-ear headphone I've used, so that's not a ding against the Vibe Duo Nero specifically.
If you don't use an iPhone, I'm not sure the price premium ($100ish instead of $50 or so for similar headphones from other brands) is worth the solid metal construction and attractive design. (The burled metal ring around the outside is really nice looking.) Headphones, after all, are easily lost. But for iPhone users who want the whole experience that the stock earbuds offer—taking calls, skipping tracks, pausing music—without the crappy sound and barely-functional design from Apple, the Vibe Duo Nero seem like an obvious choice. Just be sure you get the "Nero" model, not the regular Vibe Duo, which doesn't have the button. (But does have the microphone.)
Update: After two or three months of happy use, my Vibe Duo stopped working. Many others have reported the same issues. Considering this, I have to advise skipping the Vibe Duo Nero earbuds unless you're prepared to ship them back to V-Moda every few months for repair.
Update Update: V-Moda has changed the build of the Vibe Duo and I think they've got the durability problem licked.