Around $0.7 or so, if I remember right.
early 2011?
I'm not sure what is considered "mass adoption", but the price was around $0.10 when the first free/open source OpenCL miner was released that enabled widespread mining with ATI GPUs. https://bitcointalksearch.org/topic/python-opencl-bitcoin-miner-1334 I remember having a few % of the network hashrate with 2 5970s.
Before this, there was a publicly available CUDA (and maybe OpenCL too) miner that sent 5 btc from every block to puddinpop, the creator of the software. I think the price was around $0.06 then.
This in no way implies that there will be an increase in price when ASICs start mining, if that is why you were asking
oh I am fairly certain there will be an increase in price
