Social proof is a big thing for most buyers, and VCs are no exception. But social proof doesn't render them idiotic. And Andreessen isn't a giddy MBA herd animal, he's a guy who's built and exited with two massive startups.
But to dig into your assumption that $180m is ridiculous... The investment doesn't matter-- the valuation does. So let's guess that they sold a third of their company for that $180m-- that's a $540m valuation. Is that unreasonable? They reportedly have a run rate of $50m. I'll bet it's twice that in a year. What sort of revenue multiple do you think is appropriate for a high growth tech company? What kind of revenue/growth rate would be appropriate for a $540m valuation?
I'm all for poking fun at absurd valuations for companies that don't even have a glimmer of an idea for revenue, but these guys are looking at $50m/yr and growing like a weed. What's not to like?
[edit: another poster said a run rate of $200m - If that's true, wow.]