iPhone developers already have the beta for OS 3.1, and it has some nice improvements:
According to numerous sources, many items got some love in this beta, including Voice Control now working over Bluetooth (for iPhone 3GS users, that is). The AT&T profile has been updated to 4.2 (enabling MMS to work), the iPhone now vibrates when moving icons around, third-party apps now having APIs to access and edit videos, and the baseband firmware is now version 5.08.01. Additionally, editing video no longer saves over the original by default, allowing you to save a copy and preserve the original for transferring later. Finally, several improvements have been made to OpenGL and Quartz.
Not a huge update but a few nice tweaks. The ability to edit videos while saving the original is huge fix, though. Editing should have given you that choice in 3.0, but thankfully 3.1 should remedy that.