The GTBE backend boards came back from the PCB fabrication company and I had a chance to solder one together. The top of the board contains the data converter circuitry and the bottom contains the power supplies.
So far the board powers up without any problems. All of the OPA1632 fully differential opamp used to drive the ADC are running a little warm, but this seems to be normal based on some forum posts. A stronger substrate could have been used for better mechanical support, but for just $66 a piece for a 4 layer board they are pretty good.