In the whole first month of Buffer, we had less than 100 signups. For comparison, we now have 560,000 users (2.5 years later). We now sign up 100 people within a couple hours. It amazes me to think about it.

I had a previous startup that also started slow, but never really changed. The key difference between the two, was retention. So I would highly recommend anyone who's getting started to closely watch retention. Does anyone keep using the product into their second week after sign up? That's the first thing I'd focus on with what I know now.