Just a quick heads up to developers: Are you struggling to determine what changes between one beta release and the next? There's an easy solution. Head on over to the pre-release reference library. This site lives behind the normal Apple firewall and can only be accessed by members of the paid ($99) iPhone developer program.
Normally, Apple's documentation on the main beta release page (also behind the paid developer wall) lists only those differences between the last major firmware version (currently 3.2) and the newest beta (currently 4.0 beta 2). Over the last few days, I've been able to point quite a few people over to the document that shows the differences the previous beta (4.0 beta 1) and the current (4.0 beta 2). By checking in there, you can easily see what's new right away when a beta build drops. Hopefully this will save some of you a bit of extra work.
Thanks, Emanuele Vulcano!