Apple has just informed developers that a new version of iPhone 3.1 Beta firmware and SDK have been released:
iPhone SDK 3.1 beta 2 and iPhone OS 3.1 beta 2 are now available on the iPhone Dev Center. These versions are for development and testing only and should be installed on devices dedicated to iPhone OS 3.1 beta software development. Please read the iPhone OS beta Pre-Install Advisory and the iPhone SDK 3.1 beta 2 release notes before downloading and installing.
Use the Apple Bug Reporter if you discover compatibility or functionality issues while testing with the iPhone OS 3.1 beta 2 release.
Registered developers can, as stated, grab it via developer.apple.com.
UPDATE: Ars Technica reports iPhone 3.1 Beta 2 allows developers to send apps to test devices via Wi-Fi, rather than having to tether via USB as in previous releases.
According to WhenWithApple, minor changes include new language for the video editing options, now called "Trim Original" and "Save As..." Screenshot after the break!
When/if we come across anything else, we'll update and add it to our ongoing iPhone 3.1 Beta Walkthrough...