The iOS 4.2 update will actually reach the public on Tuesday, November 16th instead of today, a Greek news site says. Though only citing a "reliable source," iPhoneHellas is thought to have a good track record with iOS release dates. Providing some backing evidence is a German site, which claims that references to November 12th were removed from carrier bundles.
The delay is likely connected to a critical Wi-Fi bug discovered by iPad users running the iOS 4.2 gold master. Connections may drop after a just a few minutes; on top of this, some people have had problems loading Safari. The Wi-Fi issue was discovered just recently, which may have forced Apple to scramble for a fix.