Most likely the extra hashpower is from failovers BUT yes, those mining here SHOULD increase their hashrate as I have but to have that great of an increase overnight is definitely NOT miners adding extra power...definitely failover and/or slush pool received some immigrants from Ghash.io. On another note...slush pool "size" has supposedly dropped 1% according to https://blockchain.info/pools, we were hovering at 4% for the last couple weeks, very strange.