Paul Haddad of Tapbots confirmed that Apple is rejecting apps which send out UDIDs. The developer posted a rejection notice for version 2.2 of its popular twitter client Tweetbot. The notice says that Tweetbot was rejected because the "app does not obtain user consent before collecting their personal data" and points to the UDID as the culprit.
Tapbots says it was using the UDID for its push notification service and has disabled the code in the most recent version of Tweetbot that it submitted to the iOS App Store. Haddad advised other developers who rely on the UDID, "If you are an app developer and depend on UDID for any functionality it's time to migrate away from it, sooner or later Apple will catch you."