I feel that Bitmain is skimping on the PSU.  Assuming that they're using Enermax ERV1000EWT-G 80 Plus Gold which is approximately 90% efficient at around full load (996W or 83A total on the 12V rail), the S2 would be drawing around 900WDC (1000WAC at the wall*90%) from this PSU.  That's a 90% (900W/996W) continuous load 24/7.  That's too close for comfort.  A 1200W PSU (75% load) would be more appropriate.  Personally, I prefer a 1500W PSU (60% load) for the S2; much closer to peak efficiency which is at 50% load.

Bitmain should offer an option to sell the S2 without a power supply at an appropriately reduced price so we could supply our own PSU just like with the S1s or get rid of the relatively puny 1000-Watter and use at least a 1200W premium PSU.  The cost difference for them shouldn't be that much especially when purchased in bulk.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817194101