I recently bought a pair of these, and this is the story as far as I am concerned. Experience base goes from Etymotic's, through the Shure 535's and IE8's (Although I suspect my IE8's are knock off).
I went to a high end store where they would let me listen as they had spare tips etc etc, and paid £595. They are the IQ9 model. I saw them and thought that an Ultrasone IEM might be interesting so I had a predisposition to wanting to like them. I listened to some Ultrasone over ears in the same store a few weeks before, and wasn't impressed by the sound, but was by the build quality, I can't remember what they were, magnetic planar things that came in special editions with fancy titanium swirls and stuff, came in a wooden box about as big as a tea chest. So even though I had a poor experience with the brand, for some reason, and reading some reviews on here an IEM offering from them peaked my interest.
I brought my C4 to the shop with me so I could hear them through what would be my main source. I plugged them in at the shop and after about 30 seconds took them out and told they guy that there was no bass whatsoever and I really wasn't interested, as much as I wanted to like them, my ears told me no. I have pretty big ear canals it seems. He suggested that the lack of Bass was that I didn't have a perfect seal and scurried off to find some fatter tips which he did. As soon as I got the correct seal I handed him my plastic. There was a lot of Bass there, but totally non existent without the seal, and I have noticed that even the slightest hint of a gap and the amazing bass vanishes.
Then I got them home and spent some more time with them. I considered taking them back but circumstance would dictate that I had to travel so I just took them with me and hoped that playing around with different tips and positions to get a seal would improve what was a bit of an unsettled sound really. It was almost as if they simply couldn't process quickly enough, they seemed not to be keeping up with the music although there was suggestion that these things could be something special at times. It was quite confusing, but I persevered.
Then they just got better and better and better and better. At first the bass was just plain lazy and sloppy, but certain tracks would sound good, they were really inconsistent for at least 100 hours I would say. The details were there but not separating enough, the sound stage was there, and sometimes it was massive for IEM's and sometimes it tightened up so much that it made me think that these were a waste of time and a waste of money.
Now they seem to have settled into what I consider to be the best IEM that I have ever heard, I haven't heard that many though so please bear that in mind.
I find the detail to be amazing, and the sound stage even better, this was really brought home more when I used them with my Mac Air only for watching a TV Series (House of Cards)...all of a sudden, as it was not swamped by music, the sound stage became clearly apparent with sounds coming from where they were laid down in the track, really impressive stuff straight out of a Mac.
They do have an amazing sound stage for music also in my opinion, although it did take some time for this to fully settle. Now the instrument separation and the details are simply incredible to my ears, and the bass is lovely.
I would describe them as Ultra refined. Amazing to hear how they completely change when I change the EQ on my Colorfly, really responding to the different demands.
I don't get a massive feeling of a warm sound, they seem more technical than that, they seem to achieve many things, but tiring they are not, there is still a certain amount of reservation if you like, they don't punch any one frequency above others in my opinion, they are so very very balanced.
Incredible to listen to stringed instruments, and as mentioned they almost take away from the visuals when using them for audio from a video, they are that impressive. To be honest I kind of have an admission and a comparison. This is my second go round with House of Cards, first time I watched it on my top shelf surround sound kit at home, to be totally honest the sound coming straight out of my mac into these was much more detailed, you could really hear the separation more, exactly what the recording engineer was up to, it was interesting and ridiculously detailed.
Maybe people will say that of course this is the case with all IEM's, I don't know, but they are very different to my Shure 535's, another league I would say.
Kind of glad I had to travel now and didn't take them back.
Maybe it just my Dumbo ears, but the fit really really works for me.
They are beautifully built, there is no questioning that, the build quality is the best I have seen or felt for IEM's, like little tanks.
I find the cable and the way they have coated the bit to bend around your ear to be ultra comfortable, after a while it just sits in the perfect shape, they hook on and press in very quickly and with minimum fuss.
I am not very experienced with IEMS's, but I really really like these and genuinely think that they are worth the money. In my opinion the sound quality is beautiful, I have them in right now, and they still blow me away. Very happy with them, although the relationship got off to a rocky start.
I love the lows and mids on them though 
Too bad I'm sending them back this week... Swivel cable like the UE900 and Shure models... It's a little stiffer than the UE900 cable though.
The IQ has a nice fun, V-shaped signature 
