What I love about the contact book on Android is the ability for it to link my contacts to their Facebook pages, and use their profile pic as their contact pic. With Ice Cream Sandwich, and still the same situation with Jelly Bean, this functionality is removed. I can still link profiles to my contacts, but things like their profile pic isn't pulled in to their contact page.
This is where HaxSync comes in. It adds the ability to sync friends and Facebook events to your ICS phone. Contacts will have their Facebook profile pic etc imported, and Facebook events will be synced to your calendar.
Just download and install it, and then in the Accounts and Sync settings, it can be configured there. A nice feature is the "fuzziness" of your contacts names. You can change how much of a match the names can contain before getting linked together, so if your friend's called something slightly different on Facebook HaxSync will still link it together. This was a pain in GB ROMs where if the name didn't match up slightly, it had to be linked together manually, which meant having to sync your entire list of Facebook friends to your phone first.
The app isn't free, but for the small price to pay it does fix my only gripe with ICS.
Edit: After upgrading to my HTC One S, I found that this app isn't needed if you stick with HTC Sense. HTC Sense for Facebook that comes with Sense still includes the full Facebook integration.