A great presentation about design API and software packages: http://python-for-humans.heroku.com/
Even if you’re not into pyhton (like me) worth to read 
It lines out once more the importance to focus on usability and users (yes, other developers might also be your users 
). And to focus on keeping the effort to get started as low as possible. And a lot more important stuff.
Thanks a lot to the guys behind binärgewitter for pointing me to this gem.
Why this post is in english? I dunno. Just felt like doing so Wasn’t the first.