This is a little out of date in some respects, but with recent events it may come back sharply into focus soon. I was curious to see just how much Silk Road was contributing to what was a strong underlying growth trend in Bitcoin price - and the answer seems to support the claims that it was almost entirely responsible (more than I expected, see below).
I doubt there's many people that believe Bitcoin got to the current giddy heights through mass adoption or genuine utility, so the next question is what happens to Bitcoin if the factors driving it up there disappear along with Silk Road?

Correlation != causation
This, both price and silkroad user number are expected to rise with bitcoin adoption (and thus time). I bet there are other services/metrics that show a similar correlation with the bitcoin price (bitcointalk speculation posts perhaps). You can't conclude from this that silk road is the principal driver of price.
As far as I've seen, most people accept already that silk road was an important driver of the demand for bitcoins (outside of speculative bubbles), and so the price, the surprise is just how tight the relationship appears to be.
C'mon, you know it's true really....