> I would break up the 20 lines of command-line commands.

I would have to find a compromise for this, because on one hand it's convenient to have all the commands in a single place (so it's easy to get an overview), but on the other hand that block includes several logically different operation (importing, grafting, merging) that would deserve their own "FAQ".

> I would also state (or link to) something about forward-porting from
> 3.x to 3.y and that 2.7 should be kept separate (both of which I
> think the current patch assumes knowledge of).

This is currently explained, but should be reorganized and integrated with my patch.

> I would also say (or link to) something about pushing all branches 
> simultaneously.

This happens automatically, so I don't think it deserves more than a short mention somewhere.

> Lastly, might it be worth explicitly dividing the Mercurial stuff
> into separate sections for (1) everyone, and (2) committers? 

ISTM that all the things that contributors need to know are already explained somewhere else in the devguide.  This includes cloning, switching branches, and applying and generating patches.
What I'm described here is mostly aimed to developers, since contributors don't have to commit/merging/grafting and dealing with all the related things.