At the moment, I have had limited success in private groups. I can certainly "mostly" catch up with other pilots - Mr Stabler and the inimitable Zaphod ViperTaxBrox chaps when in a private group and in a quiet location (such as a nav beacon).
We have had issues when one pilot goes out of range, trying to find a way back to the other ships and them not appearing when you do. Also had the infamous rubberbanding and occasional timesliced ship damage problems.
We have been able to meet, to test voice and text comms and to share limited amounts of team bounty hunting but beyond that, there's not much to report at the moment.
We've been able to ticket a few bounty irregularities, the crazylegs Viper landing gear deployment sync problem and a cargo scoop/drop/scoop problem, so we've been able to further the testing of the game, but we couldn't really call it co-op gameplay YET.
Looking forward to how it improves.