I bought a refurbished Momentum from Amazon for slightly more than €200.
I had already tried the Momentum at the Apple Store, but that's not exactly the ideal environment to try out a headphone
Now that I have them at home, I can already say that the Momentum is indeed the best portable I've tried. For me, it easily trounces the HD25 and the Amperior (sibilant, too metallic), the KEF M500 (no bass impact, too much emphasis on upper mids), and the V-Moda M-100 (too much bass, at the expense of mids and detail) in the same price tier. I don't know why the Momentum is marketed as a laid-back headphone for relaxing. This thing has impact and energy in spades. The bass is outstanding in quality and quantity; I guess it can be too much for certain genres, but I don't find it as invasive and overpowering as in the V-Moda M-100. Vocals are almost perfect. There is a hint of sibilance in the highs, but it's just a hint; the Momentum will never make a track more sibilant than it is, as will happen with the HD25 or the HiFiMan HE-400. The detail is much better than I expected, and the same goes for the soundstage. In the Apple Store, the Momentum sounded more congested than it really is.
The overall signature of the Momentum is smooth and musical. I'm finding it perfectly suitable to most of my music. As I had already suspected, the Momentum is very close to an over-the-ear version of the Senn IE8 - and for me, this can only be a good thing
Aestethically it's wonderful, but I guess everyone knows this already
I got the brown version; I like the black cups and headband, but the red threads and cable spoil the effect for me (V-Moda got the all-black look right).
If I have to find one flaw, it's the clamp. It's not as tight as the AKG K518 (K81 in the US), but it does hurt a bit.
I don't see myself letting this headphone go for a long, long time