Apple's latest software update for its various mobile devices was released this past month on the 22nd. The 4.2 update brings a few interesting features to the iPhone, iPod, and iPad. Features such as Airplay, Game Center, and Multi-tasking. These 3 features are the ones that I've personally found the most useful so far, but there are other improvements as well.
Airplay gives you the ability to stream all media directly to compatible speakers and devices. No longer must you plug in your iDevice to your stereo to play your music, or videos. Just send it over the air!
Game Center is apple's solution to online multiplayer gameplay. Tired of having to register accounts with OpenFeint or Crystal? Just use Game Center. Since it's by Apple, you don't need to register all over again, it just uses your Apple ID and password. Thankfully, many games using Crystal and OpenFeint now allow you to use your Game Center account instead.
Multi-tasking means you can now run multiple apps simultaneously. No need to stop playing music while you work, or close out Safari to check your Calendar.
For me, AirPlay and Multi-tasking take the cake. The other features are just bonus.
For more info about iOS 4.2 features, go to: http://www.apple.com/ios