Llama no longer supports having different volume settings within the same profile (I would set my notifications to low volume while I'm sleeping, but keep the ringer the same - can't do this anymore).
I, too, had to redo all my contact links. Also all of my general sound settings (ringtone, notification, etc).
Also, I think ~12 of my apps immediately prompted for updates, to make them compatible with ICS.
Definitely not a fan of them switching the "cancel" and "ok" button positions on most of the system pop-ups. What's the point?
Had to enable the wireless network, and reset the phone, to get it to pull down a data signal after the upgrade.
I do like the "app association" option in the phone settings. Also, I was happy to be able to disable Facebook messenger, but disappointed that I can't do anything with the stock bloatware (Slacker, HTC messenger, etc).
After all the hype, I'm actually not entirely sure why this is so much better than GB - but I'm looking forward to figuring it out.