This new firmware brings many new (awesome) feature to the Playstation 3. These include custom soundtracks, a all new trophy system and the ability to use the XMB (or the PS3's home menu) while playing games, so you can reply to messages without quitting.
For more info check out these links:
http://blog.us.playstation.com/2008/06/29/firmware-v240-walkthrough-part-1-the-xmb/ Walkthrough Part 1
http://blog.us.playstation.com/2008/06/30/firmware-v240-walkthrough-part-2-trophies/ Walkthrough Part 2
Australia - http://au.playstation.com/support/ps3/faqs/ps3_update_tsc