I've been watching this for months. It's been exponential the whole time. I think this trend will continue until bitcoin awareness reaches saturation point, after which, it will level off.
I expect the value of bitcoin to trail this graph.
At a comparison, Facebook has been increasing quickly since the beginning in 2004-2005, and is just now starting to level off (arguably).
Bitcoins have only been mined for a year now, maybe a year and half, right? Considering half the forum posts are May or later roughly, it's only starting to take off.