It looks like the pure-Python fallback implementations were a big deal for the (nearly resurrected) Jython project, in particular:

http://fwierzbicki.blogspot.com/2009/02/progress-with-mercur...

I was hoping that the bookmarks extension would be fixed to allow true, local, lightweight branching. Looks like I have to wait for a future fix.

The problem with bookmarks now is you can't selectively push from a bookmark (ie: only push the changes from one bookmark and not the others)

    hg push -r bookmarkname

does exactly what you want.

me too

I'm a huge fan of the pure Python piece-- it allows us to integrate it much more easily with our cross-platform Python embeds.