Though quite sweet, the price of the Pegasus is also quite dear - coming in at like 2400 bucks. That is like $400/drive.
I haven't built anything with thunderbolt, yet, I have built a SAN
with 4GB Fibre Channel Host Bus Adapter, which hit $150/drive ( at 20 drives ), and in some tests achieve 365MB/s using Intel's NASPT test suite, not IOMeter - NASPT produces numbers that are much closer to real world performance.
What I learned was that under different read/write scenarios speeds vary wildly.
There are two thunderbolt ports on the Pegasus, this is there to allow you to daisy chain several pegasus boxes off your host machine.
Should also point out, that the Pegasus provides Direct Attached Storage (DAS) and at this time is not reachable from the network without traveling through a server, which means you'll only get that 780MB speed on one machine.