Hey Joel,
I'm interested to know if the first 100 users stuck with your product over time or you had to figure out how to do retention over time.
Just had a look at our cohort analysis. Happy to let you know that 16% of the December 2010 cohort (those 100 people) are still using Buffer today (27 months later). It's actually fairly representative of what our retention stabilizes to after 4-5 months for almost every cohort, though 100 is not an ideal sample size!
We've certainly worked to improve retention over time, but in addition I think with Buffer I finally had hit upon a problem that was a real pain point. So, there was good retention right from the start.
I custom-built my own cohort reports but as number of users grow in my own app, I'm planning to replace it with MixPanel. You don't really want to put stress on your own database servers which are meant for production, not for analysis.
Not even a blurb on there.