I have been using openfiler for sometime. I've been using it primarly as a nfs datastore for vmware.
I did some basic benchmarks against a netapp storevault, and the Openfiler outperformed it on speed.
cifs and Active Directory work well
Nic teaming seems to work well if configured correctly.
jumbo frames is supported.
updates are frequent and easy to apply
snapshots work ok, but degrades performance. I havent' been able to find a good way to revert back to a snapshot
HA/Clustering can be difficult to setup
I haven't had a need for anything other than a NFS datastore, so I haven't pushed its limits yet..but for what I use it for, it works very very well.