iPhone SDK 3.1 Beta 2 Available Now
I'd say that pretty much sums it up. From the comments I've seen and the look of the beta, this is most likely the gold master of 3.1 - meaning you can expect 3.1 to be released pretty shortly.
Among the changes listed are quite a few APIs for customizing video/picture control looks, so expect a ton of nifty looking apps accessing the camera coming out.
The baseband has also been updated in this release to 05.10.01. Read: unlocked folks, or people who want to unlock in the future, don't be upgrading yet.
iPhone Dev Center