A log trend line (more precisely: linear regression on log charted price history) is a nice little tool to get a feeling for where we are at any point in time compared to the historic trend, and where we're going to be, very very roughly, in a few months or a year from now.
I don't think Bitcoin's long term trendline is going to be straight on a log graph - I think it's going to trace an S curve
graphed in log space.
http://bitcoincharts.com/charts/mtgoxUSD#igDailyzczsg2011-11-01zeg2013-12-30ztgSzm1g10zm2g25zlThrow away the data from before November '11, while the exchanges were trying to figure out how to operate, and what do you see?
I know, I know

I participated in the previous discussion of that idea. Didn't we conclude that the well known S shaped "tech adoption" curve would still be a straight line when mapped to log. Why does BTC deserve a "super S", if I may ask?
I don't exactly know what super S means, but anyway, bitcoin adoption is both about the network effect, or each user spawns 2 new users after a unit of time, plus the fact that each user seeks to expand his bitcoin hoard as he understands or gains trust in bitcoin as a store of value. In serious questions like this, understanding and logic is not enough, your feelings and intuision have to be on board also. Hence, the price function could increase at a higher rate than number of users. Impossible to be certain, also after the fact.