built a quick spreadsheet showing average block duration and difficulty adjustments as percentages for the past 2 days using http://blockexplorer.co/ data.
only have from block 42201 (last difficulty shift) as http://blockexplorer.co/ is currently down (really wish it included total network hash rate)
with a block target of 2.5 minutes, red numbers are below the target (diff too easy), green above (diff too hard)
Thanks for this info. I had estimated off hand previously that the difficulty adjustment was based on an average of the last 100-200 blocks, giving it a slight delay that is more pronounced with the low hash rate.