Why only startups? Wouldn't it be interesting to know what non-startups use?

I can see how it wouldn't be all that useful to have a full stack of Oracle and Peoplesoft, but a lot of big companies are built on the same stuff that startups use.

If anything (imo), startups are the least interesting company size / maturity when looking at technology stacks, since they have neither grown enough or been around long enough for their choices to actually matter,

(on the other hand, really large/mature companies are likewise uninteresting, because their choices are almost certainly entrenched in historical BS and legacy nonsense.)

We would love to have some bigger companies as long as they still try new things. For bigger companies we might do it by product. Instead of Google, Gmail and so on

You should add http://weusethat.com/ to the description of the repository and as the url of the github user (not an org?). Right now there is no link to click!

Good point!

Something I'd like to see is also the personal setup of the interviewee(s), for example, coding environment or Mac/PC preference.

Don't know if you are already aware of http://usesthis.com. Some of the developers they interview get pretty in depth with their setups.

Definitely definitely put that at the top of your front page!