As always, beta SDKs remain behind an NDA wall, so we cannot post specific details about changes. Developers will find full release notes and update read-me's at the site itself.
A final warning: If you plan to seek alternate means of acquiring and installing 4.2 beta firmware for iDevices, don't. You may very well render your iPhone or iPad inoperative. The OS will not work without an accompanying developer certificate.
Good luck and happy developing.
Thanks to everyone who sent this in.