Twitter's updates are most newsworthy since they bring push notification and multiple account support to Android. User with multiple Twitter accounts will be able to easily switch between their accounts. Other changes include an updated home screen widget and other improvements and bug fixes.
The updated Facebook app for Android adds Pages support improvement that lets you view the full list of pages you like as well as Pages you administer. You can also post as a Page you administer.
If you haven't updated yet, check out your My Apps in Market or your phone notification bar.