iOS 4 device compatibility

Just heard from one of the folks we know who updated his iPhone 3GS to iOS 4 yesterday only to lose his AT&T data connection completely. Today, when he could no longer even place calls, he contacted AT&T who, after several escalations, informed him there are isolated incidents of iPhone 3GS on iOS 4 with unlimited data plans no longer being able to connect to the network.

They told him they're working with Apple to fix it, and put him name on a contact list so they could let him know when it was resolved.

Our question is -- how isolated is isolated? How's your AT&T unlimited data post iOS 4 update?