The application will let you know any time you receive a message, when someone wants to chat with you, when it is someone's birthday, etc. These message notifications pop up on your locked screen so that you can respond to them quickly.
Some interesting features include the ability to share URLs without having to jump to a browser while using Facebook, easily select the privacy posts' privacy settings, and share posts on your friends' walls.
In addition to that, now it is much easier to add friends to your favorites, get rid of contacts on friends list, upload tons of photos at once, check out whatever photo that you've been tagged in, and upload pics to groups and pages.
FriendCaster for Facebook is a great alternative to the official Facebook version and its top asset is the excellent interface: alluring, practical, and useful.