Ask HN: How many people small tutorial-like eBooks useful?

I've been using small eBooks for different topics (such as http://guidetodatamining.com/ for data mining) and I've been finding them amazing.

I was curious to see how many people are actually using them?

Would a Wiki-like or Git-like platform with many, many small books on different skills or topics be useful? Something that goes beyond a Wiki article, more hands-on, but shorter than purchasing an actual book and allows collaboration?