Yesterday, an update was pushed to Thunderbolt equipped Macs under the name Thunderbolt Update 1.2. This tiny update is only required for compatibility with the Thunderbolt to Ethernet adapter, which was announced at yesterday’s WWDC keynote. While this update has very little purpose for most Mac users, it’s causing big problems for some.
Today, users who have updated their Macs via System Update have reported boot failures after installing the Thunderbolt update. The errors range from kernel panics to “unexpected error” messages. Currently there is no fix for the issue, so those affected are forced to reinstall OS X Lion. If you have not yet updated, we would advise you to hold off until a fix is pushed.