Difficulty has just jumped 5%, some 14/16nm chips are being turned on?
Don't underestimate the size of the daily or weekly variation in hash rate due to statistical noise. The hash rate regularly varies by 10% to 20% from day to day solely due to statistical variance. It is only over a week or longer that actual changes in the hash rate become clear.
You can expect the hash rate difficulty changes every two weeks to fluctuate within a range of about plus and minus 2-4% solely due to statistical noise even if there is no change to the total actual network hash rate.
It is only over months that long term trends are clearer.
The mathematical details.
There is a 10 minute block average solve time with a 10 minute variance (poisson distribution). So the standard deviation percentage error in solve time is 100 / sqrt(number blocks). Most of the time the difficulty change will be within 2 standard deviations.
There are 2016 blocks found on average between each difficulty change so for each change the standard deviation is 100 / sqrt(2016) or about 2%. Two deviations are 4%. So hash difficulty changes may be frequently in error by 2% and possibly as high as 5%. So don't be surprised by a 5% change. It may simple be due to the previous fortnight being 2% or so under and the next 2% over.
