Apple introduced the 3.1 upgrade recently, and of course I had to try it.
The 3.1 version included amongst others:
* Genius Recommendations for Apps
* Genius Mixes
* Download Ringtones Wirelessly
* Organize Apps in iTunes
* Improved syncing for music, movies, TV shows, podcasts, and photos
* iTunes U content organization
* Redeem iTunes Gift Cards, codes, and certificates in the App Store
* Display available iTunes account credits in the App Store and iTunes Store
* Save video from Mail and MMS into Camera Roll
* Option to “Save as new clip” when trimming a video on iPhone 3GS
* Better iPhone 3G Wi-Fi performance when Bluetooth is turned on
* Remotely lock iPhone with a passcode via MobileMe
* Use Voice Control on iPhone 3GS with Bluetooth headsets
* Paste phone numbers into the keypad
* Option to use Home button to turn on accessibility features on iPhone 3GS
* Warn when visiting fraudulent websites in Safari (anti-phishing)
* Improved Exchange calendar syncing and invitation handling
* Fixes issue that cause some app icons to display incorrectly
But it also included the usual problems. After updating I have to reconstruct the settings for my cellular data network and also the MMS settings. Another problem I discovered was that it changes all ringtones to the default ringtone.
There has been rumours that the upgrade mess’ up the battery of your iPhone, whether or not these problems are true, I for one have not had this problem.