This morning’s Thunderbolt update might have left a lot of rooted users scratching their heads as to whether or not to take the plunge, but fear not: you haven’t been left behind. That rooted update we saw last month over at XDA is the same build number we are seeing OTA today, and brings with it all the benefits and none of the unrooting. Again, we recommend all rooted users steer clear of the update being pushed to your handset and instead grab the rooted version at the source link. There, you’ll find the file and instructions on how to flash it to your Thunderbolt (s-off and through hboot, not recovery), all the while maintaining precious superuser status.
Source: XDA Forums