Apple has made iPhone firmware update 2.1 available for download.  This is a 237.8 MB download through iTunes.  Apple is stating that there is a new SDK to download, although it is build 9M2517 (which I think is the same as the old SDK), there is a new developer download iphone_sdk_for_ iphone_os_2.1_final.dmg.  It remains to be seen what (if anything) has actually changed in the SDK itself.

As you can see from the 2.1 firmware photo, there is a list of bug fixes and improvements.  They are as follows:

• decrease in call set-up failures andcall drops
• significantly improve battery life for most users
• dramatically reduced time to backup to iTunes
• improve email reliability, notable fetching email from POP and Exchange accounts
• faster installation of 3rd party applications
• fixed bugs causing hangs and crashes if you have lots of 3rd party applications
• improved performance of text messaging
• faster loading and searching of contacts
• improved accuracy of the 3G signal strength display
• repeat alert up to two additional times for incoming text messages
• option to wipe data after ten failed passcode attempts
• Genius playlist creation