If your iPhone was connected to an Exchange server for email, contact or calendar synchronization prior to your upgrade to the 3.0 software, you may have run into the same problem that was bugging me for a day or so: the timeout on the passcode lock gets set to "Immediate," forcing you to enter the code almost every time you pick up the phone. Secure, sure, but very annoying. Going to the usual settings location to adjust the timeout shows no choices other than the insta-lock; what to do?
A thread on the Apple discussions boards points to the answer. Since the ActiveSync link to the Exchange server controls some security policies on the phone, you need to refresh those controls; the easiest way to do that, short of deleting and recreating the Exchange account, is to turn off all three sync modes and the Push setting. Once that's done, you can go back to the passcode lock screen and disable the lock or adjust the timeout. Put your sync settings back the way they were and your changes to the passcode config should remain in place.
While this is an annoying quirk, it's not all gripes and grimaces in the Exchange support department. At long last, users of Exchange calendars can send meeting invitations (hallelujah!); Exchange 2007 users can even view the reply status of attendees. Users can specify additional mail folders for sync, and Exchange 2007 users can search server-side mail from their devices.
For a full rundown on the enterprise-friendly features of iPhone OS 3.0, check out the Enterprise Integration guide via Apple's enterprise features page.
Thanks to everyone who sent this in.