The message appears to be that it's a combined ("converged") primary and backup appliance. Their snapshotting technology allows backups to be created instantaneously--- and it sounds like they have some disaster recovery features for offsite backups, too. They position themselves as an alternative to both Equilogic (the primary mover in iSCSI) and Data Domain (for backup.) It's a little interesting that they are not pushing too hard on the performance story (although their literature does mention it), instead focusing on the cost savings of not having a separate backup appliance. I couldn't find an IOPS number yet or other workload measurement; their front end is 1GbE rather than 10GbE, although they claim to be "10Gb ready", whatever that means.
I know at least one person at Nimble, from grad school. Good luck, guys, and congratulations on the launch!