Here's a quick summary (you can read the whole transcript, or listen to the podcast, at Blizzard's site):
- ICC is designed such that the final boss in each section is harder than the rest of the section (Putricide, Blood Queen Lana'thel, Sindragosa, and the Lich King).
- The ICC zone-wide buff "won't come in until at least a month after the Lich King has been released," which means we could see it soon, since the Lich King fight opened up February 2nd (although the devs mentioned in the Twitter chat that it's not quite time for the buff yet). It will improve "roughly once a month," and the buff will affect health, damage, and healing (much like the Luck of the Draw buff from random dungeon groups).
- They thought the Illidan encounter in Black Temple, back in BC, was a bit anti-climactic, so they wanted to make sure the end of the Lich King was "super special."
- In answer to "what next after I clear ICC:" ICC hard modes, and to a lesser extent the Ruby Sanctum, which is coming in a future patch. Ruby Sanctum will hold "roughly Lich King level gear," as has been mentioned elsewhere.