∞ Everything You Possibly Need to Know About iOS4
Covers everything that is new, in depth, across seven pages.
∞ AT&T Tethering Arrives With iPhone OS 4.0
The latest beta release of iPhone OS 4.0 now includes a configuration screen to setup internet tethering with AT&T. It's assumed that AT&T will finally allow tethering for its customers after the official release of iPhone OS 4.0 this summer.
∞ Boy Genius Report Details New iPhone OS 4.0 Beta 3 Features
Brings the first sign of widget style functionality to control the iPod app (or other third party music apps?). Since there have been no releases of iPhone OS 4 for the iPad, this widget functionality could be expanded to bring back Weather, Stocks and other missing iPhone apps to the iPad.
∞ Apple's iPhone 4.0 to Include Multitasking
BGR:
“A few new ways” to run applications in the background — multitasking.
They also speculate that iPhone OS 4.0 will only be available for iPhone 3G and 3GS, which seems to be a pretty safe bet.