A few days ago, I sat down and read through the entire user guide. It's put together fantastically, great job on that. During my read-through, I found a few typos or small things that may have changed over time that you may want to resolve.

http://esotericsoftware.com/spine-basic-concepts#Slots
The slots in the text are not in the image shown. This lead me to be a bit confused to start.

http://esotericsoftware.com/spine-tools

Right clicking anyway in the editor area will toggle between the current tool and the last selected tool.

(probably meant "anywhere")

http://esotericsoftware.com/spine-tools
"spine weights" view link is invalid, should probably be http://esotericsoftware.com/spine-weights

http://esotericsoftware.com/spine-key-frames
"IK Constraints" link seems incorrect.

http://esotericsoftware.com/spine-dopesheet#Timeline-position

A frame can number ban be typed

(probably meant "A frame number can be typed")

http://esotericsoftware.com/spine-weights#Weights-tool

It is almost always more intuitive to adjust weights only be adding influence.

(probably meant "only by", but not sure, really.)

Hope this helps. I think the only thing that could use a bunch more content is the IK section, preferably with a few GIFs to show different use-cases and benefits of them. After playing with a bunch of examples and videos watched, I still feel like I'm missing a bunch of important information on when/how to use that system past the basics of foot placement for uneven grounds, and perhaps hand placement for weapons.