Medium, the blogging platform created by Ev Williams, has just take on a big new chunk of investment:

Medium, the publishing platform hatched by Twitter co-founder Ev Williams, has raised $57 million in a round led by Andreessen Horowitz.
It’s the three-year-old company’s second funding round, and people familiar with Medium say it places a $400 million pre-money valuation on the startup.

Those figures alone are interesting (but then, a bet on the guy who co-founded both Blogger and Twitter doesn’t seem like a bad bet, does it?). But just as interesting are the figures quotes on content creators and users:

Content creators:

Williams and Medium are famously averse to talking about metrics, so the only one you’ll find there is that 20,000 people are creating Medium posts each week; Doyle tells Re/code that that number is up 4x in the last year.

Users:

In May, Medium said it was attracting 25 million unique visitors a month.

That puts Medium squarely back in the old model of a “superuser” community, where the 90/9/1 rule of “lurkers/occasional posters/superusers” applies. Not a surprise, pehaps, given that Medium is at its best with long form content, and only a proportion of people are ever motivated enough to write long form.

The interesting bit is that, by riding on top of Twitter’s social graph, AND creating an internal social graph derived from that, Medium is making it much easier for new or occasional writers to find audiences.

My own experience is that putting a post on Medium brings me less traffic than a post here – but this blog has been going well over a decade and I have an established audience. Medium’s social features are far more useful to an emereging writer looking to find some readers.

It’s going to be very interesting to watch how this develops – and how they monetise.