Actually, I found the hashrate chart too,
here. A double exponential fit on the curve since November, shows that the hashrate right now grows about 51% every month (that's a 1.5 multiplier every month).
More exactly, the prediction is HR(x) = 4282*(0.8287.^x)+1405*(1.5378.^x) where x is the month index since Nov. On June 20th (x=8), I expect the hashrate to be ~44900 GH/s.
According to this calculator, for a 50% monthly hashrate growth, the return on mining is getting minuscule. If I was to start mining right now at 150 MH/s and pay 0 electricity, I'd be mining about 3.56 ETH in the first month, and only 0.04 ETH in the 12th month ...
Is that accurate or am I missing something?