+1 for short description of what your app/website does on the front page:

"If you don’t tell people what to say about your app, they’ll come up with it themselves and sometimes it’s inaccurate or crappy."

I temporarily fell victim to not telling visitors what my site was about and (un)surprisingly they did not understand it from the interface. This happened early on when I was sharing it with people; probably what happened is that they arrived at the site and promptly left because they could not figure out what it did.