Now that GTA IV has gone gold GameSpot has had time to interrogate a couple of Rockstar Games employees and has shared some new info in the article as well:

• Completely controllable skeleton (ex: can move all five fingers).
  
• The lighting in the game has opened the door to "more cinematic cutscenes".
  
• The animation team is double than San Andreas animations team.
  

There are some more technical details within this article if you care to read, there are also some new screenshots as well.

Link: Grand Theft Auto IV Q&A: Animating the World