Something equally impressive is Facebook's growth last month, which was around 21% (according to compete). For a six-year old site as massive as Facebook to experience 20% growth in one month is tremendous.
Thanks for the support from everyone on Hacker News!
1) Release something fast. Don't wait til it's perfect. Wait til it does one quanta of usefulness, and release.
2) Work on it tirelessly. Every day, all day. Well, take breaks, but you know what I mean. Treat your time as if it were worth $200/hr, because if you're a founder then it really is worth that, and potentially a whole lot more.
3) Communicate with your users. If they email you, you email them right away, as fast as you can. If someone writes a blog post or tweets about you, address their concerns if it's a complaint or problem. It makes a difference.
We're psyched to see how the product has been taken up by users of all backgrounds, from tech savvy to never-blogged-before. Can't wait to see what 2009 holds...
For pagerank update, I actually didn't see a significant change when that happened. And most sites see a big dip in December when everyone is home for the holidays and not really getting on the computer.
But it's certainly possible that the latter came into play, especially since we just launched group blogs (and multiple blogs per account) at the time.
A lot of people are starting to use Posterous for group family blogs, and I expect that trend to only increase when we introduce password protected blogs (coming soon)
The spike itself? Announcing our funding on Techcrunch and the ensuing blog storm. ;-)
EDIT: We also did launch group blogs and multiple blogs per account. That helped quite a bit, (fallentimes jogged my memory below) since we did see people start family group blogs while at home for the holidays. I like to think of people talking about posterous over Christmas ham and egg nog.
Posterous appears to have a very large market for its product. Of course, its practice of releasing often, working hard, and communicating well has helped Posterous find a good product-market fit. But it's worth bearing in mind that lots of companies do 1-3 and still fail---typically because the market just isn't there.