I wouldn't be surprised if we see total network hashrate dip below 20 TH in the next month or two (assuming ASIC's aren't in the mix).  I for one have pulled the plug on my miners.  Even with the hardware long payed off and a decent power rate of .10 / Kwh, I'm paying $9 in power costs to make $10 in BTC.  Just not worth the effort/aggravation.  I think in the next week or two, more people will see that and only folks will really low power rates or FPGA's are going to stick it out.