Yes, vSphere 5.1 is GA, along with vCloud Director 5.1.
You can check out the What's New in 5.1 here:
http://www.vmware.com/files/pdf/products/vsphere/vmware-what-is-new-vsphere51.pdf
Several interesting new features,
vSphere Distributed Switch – Enhancements such as Network
Health Check, Configuration Backup and Restore, Roll Back and
Recovery, and Link Aggregation Control Protocol support and
deliver more enterprise-class networking functionality and a more
robust foundation for cloud computing.
vSphere Data Protection – Simple and cost effective backup
and recovery for virtual machines. vSphere Data Protection is a
newly architected solution based EMC Avamar technology that
allows admins to back up virtual machine data to disk without
the need of agents and with built-in deduplication. This feature
replaces the vSphere Data Recovery product available with
previous releases of vSphere.
Interesting since I am in the process of implementing Avamar at my current customer. A more detailed post on that to come.