After an hour and a half or so of listening, I have to say the W3 are very interesting IEMs and they have a lot of potential.
Physically, the W3 are very small and light and they are incredibly comfortable. I've been playing a bit with the tips and so far the medium Comply tips are those that fit me best. I was accoustumed to the Shure Olive tips with the Etymotic ER4S, but they don't fit the W3 very well because they are not long enough and don't provide a good fit like on the Etys. [EDIT
: I finally got a good seal with the Shure olives and they are the best tips I've used to far with the W3]. I tried the triflanges, but for some reason they sucked out some of the mids so I went back to the Complys and I'm very happy with the comfort that I get. I'm a little bit worried about the long term durability of these tips, they seem pretty fragile and I don't feel like buying new tips every month, but we'll see how it goes. The W3 pick up some hiss from the iPod when no music is playing, but it's not a big deal for me. I don't have a portable amp at the moment (well, if you don't consider a bag full of pieces for a Mini3 that I'm too lazy to build
) so perhaps this can cure the problem.
My first impressions after plugging them straight into my Ipod Touch 2G was that they don't have the "wow factor" that many headphones have. That's not a bad thing, because my favorite headphones ended up being those that didn't impress me at first: Stax Omega 2 and Sennheiser HD600. Like these two fine headphones, the W3 has a balanced sound across the spectrum and no frequency really stands out which is the key for good non-fatiguing listening. To be fair, the highs are slightly rolled off compared to most full-size cans and speakers, but that's been the case with every balanced armature IEM I've tried (Shure E4 and E500, AL iM716, UE Super.fi 5 Pro) except for the Etymotic ER4P/S which on the other hand is slightly too bright and a little bit harsh on top.
I have not listened enough yet to review the sound in detail, but I have to say that I'm very impressed so far with how they handle classical music. I've been disappointed with many headphones and IEMs in the past for listening to symphonies and the W3 seems to do the job very well, giving a "round" sound and not sounding too harsh while providing good dynamics. I'll post more impressions later...