Over 1 year IE2 update:
Cord is fraying where it connects to (FREAKING BOTH, ARGH!) housings.
They stopped burning in long long ago, but these are the impressions I've gotten:
Bass is incredibly bloated when you take them out of the box, mids don't exist and highs extend farther (ironically) than when they're full and burned in.
Bass gets more punchy, dies down a bit, but stays a bit muddy when they're burned in.
Mids come out a bit, stay pretty recessed.
Highs come down quite a bit, and soundstage retracts just like the highs do, very strange. Highs stay pretty clear. Not bright, but clear.
"Wing" tips are the most comfortable thing ever made. I've worn them for 12+ hours in a row (flight to Hawaii) without discomfort. They don't seal, so you get no isolation, but if you push them in farther than they sit with the wing tips bass becomes painfully bloated, mids come up but are very polluted by bass, and highs retract some.
I've no idea what the impedance is, as Bose doesn't believe in publishing specs, but it must be pretty high. The Zune HD's volume goes from 0-30. The sweet spot for the IE2's is definitely 18, which is pretty loud in a quiet setting, but perfect when there's a little background noise. Below 15 (50%) the bass dies down and they're more balanced, but bass is the punchiest and mids are the most "there" at 18. They're good until 20 (66%) and start losing at 22, where bass loses impact and the soundstage retracts farther. By 25, the soundstage is as narrow as stock earbuds from a Zune or iPod.
Cord is very weak. I've taken very good care of them, but the cable housing connection still broke. I have ~2mm of exposed wires now. Still works, but it makes them even less durable, and their housings are entirely (cheap) plastic.
If you have them, take some glue or electricians tape and seal the connections better, they're very delicate.
EDIT: I had to open my mouth. Left driver just died... I'm going to let it sit overnight and see if it magically fixes itself. That's really sad, I had a pair of 'stock' apple earbuds that had a much more badly damaged cable and worked just fine.