There are preliminary benchmarks from Phoronix available here:
http://www.phoronix.com/scan.php?page=article&item=talos-wor...
TL;DR Performs similarly to current E3/E5 xeon CPUs, and the 64 cores (57 tested) are great for parallel workloads. There's some applications (OpenSSL) missing POWER8-specific optimization.