I agree, the frontpage of mediagoblin.org can use some improvement. We're working on that. If you want a fast summary of things, you can still watch the video from the crowdfunding campaign we ran last year with the FSF (hell, you can still donate too!). http://mediagoblin.org/pages/campaign.html
We also have an intern helping us clean up the homepage. Things should be getting clearer soon, I think. I agree that http://mediagoblin.org/ could use some improvement.
In the meanwhile, if you're wondering what it offers, right now it already supports nice photo, video, audio, document (pdf.js!), and even 3d model support. It's written in Python, so it's easy to get hacking on. We have a lot more exciting things on the way too, most noticably federation; we currently have someone working full time on adding federation via the Pump API: https://github.com/e14n/pump.io/blob/master/API.md
This will make it so that even though there's a bunch of separate MediaGoblin instances out there that you should be able to have a lot more of the same social features of other media hosting sites as if they're in the same place.
I'm happy to answer questions if anyone has any!