The past 8 difficulty changes have been
28.4%, 23.92%, 10.32%, 19.47%, 19.63%, 35.88%, 29.4% (most recent)
see the link from here
https://en.bitcoin.it/wiki/Difficultyhttps://docs.google.com/spreadsheet/ccc?key=0AmcTCtjBoRWUdHVRMHpqWUJValI1RlZiaEtCT1RrQmcEach difficulty change is exponential, and occurs every 11 days or so, so almost 3/month
This works out to be approx 105% increase over the last 30 days
If you plug that into the genesis block
Currently we "only" have a difficulty of 65 million. With a network of 9PH, the difficulty rises to about 1.5 billion. If you sum together what the known ASIC suppliers have announced, 9PH will probably be added by early 2014.