The official SQL Server AlwaysOn team blog.
The upgrade/update guide for availability group servers is now live on MSDN.
Upgrade and Update of Availability Group Servers with Minimal Downtime and Data Loss
It shows how to upgrade/update to any major, minor, service pack, or update release with minimal downtime in multiple deployment scenarios.
This is great, but what about applying OS updates/patches to Failover Clusters running Availability Groups?