A little under two weeks, after a PG mention in an essay. Sounds like you got a similar boost from a reddit appearance (oh, if only we'd had reddit to promote on back then...). Be sure to engage those users, especially if they write you; users who care enough to write feedback -- that's gold.

Then a week or so after that, we had a splendid day - neither Steve nor I needed to submit any links, we just used the site like anyone else.

It was a good thing, too, because I was hitting my limit of aliases&passwords to remember.