@rrhoover - at the moment, I only prioritize code-related things, so bug fixes, updates, and features-to-add. My system is embarrassingly low tech: a bunch of text file todo lists with headings of "DO RIGHT NOW", "do soon", and "later".
Then I have a separate list for user feedback. I get feedback via twitter, email, and Penflip discussion threads, so I consolidate all of it into a single text file. Every time I receive similar feedback, I increment instead of adding to the list again, kind of like upvotes. See screenshot: http://grab.by/t1k6
With that, I always know the most requested features, and I have a pretty solid grasp of what the users want, so I know what to focus on.
@rrhoover to be honest I almost feel like I'm cheating at this point. I have a long list of marketing (or growth hacking :) ideas, but I haven't even touched it. People just keep signing up. No hockey sticks, but steady growth. I can't complain.
I've been somewhat vocal and transparent throughout the process, especially early on, and I think it's paid back in spades. A blog post I wrote, GitHub for Writers, received quite a bit of attention, so that drives traffic consistently, as well as some coverage by a few tech blogs (all unsolicited), and a couple posts to Hacker News. Additionally, I mention Penflip in relevant discussions whenever I can. All of that compounds.
The other big driver is word of mouth. I encourage users to share whenever I can, and they do. The great thing about Penflip is that it gets better when your friends join - you want them to check out your work and give feedback, so you pimp out your stuff.
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