By request, here is an update for interested persons on the status of the rewrite branch.
The major purpose of the rewrite branch is to implement a bot framework that uses the new MediaWiki API (see http://www.mediawiki.org/wiki/API for details) instead of the old approach of scraping HTML wiki pages. Note that many other potential areas for a rewrite have been suggested on this list, and at http://www.botwiki.sno.cc/wiki/Rewrite, but most of those are not currently being pursued due to a lack of resources.
The software in the rewrite branch currently is runnable, but incomplete, and with limited documentation. For the most part, the bot programming interface is intended to be very similar to the interface used in the current pywikipedia trunk, so that bot programs can be ported easily, but there are significant changes that we have started to document in the file README-conversion.txt. To date, most methods of the Page object that read from the wiki have been implemented; you can, for example, instantiate a Page object, get its text, and retrieve its templates, links, categories, backlinks, and so forth (interwiki links other than language links are not yet implemented). Methods that provide Site-wide lists of pages (allpages, allcategories, randompages, etc.) have not yet been implemented, but this is next on my to-do list. Most methods in the existing framework that manipulate wiki text have not yet been ported (things like replaceCategoryLinks), but these should require very few changes.
The ability to save changes to the wiki is *not* yet implemented. Note that the MediaWiki API does now have the ability to edit pages, but this has not yet been activated on any WMF wikis, so once editing is implemented in the bot framework, it still will be of limited use.
At the moment, I am doing most of the development work on this branch. Valhallasw contributed the http interface, nicdumz has contributed some user-related methods, and although he has not contributed directly, I have stolen^H^H^H^H^H^Hbeen inspired by some of Bryan Tong Minh's ideas from his mwclient project. Let me make it clear that I do not consider this "my" project by any means; anyone who is willing and able to contribute will be most welcome. It may be helpful for any new contributors to announce which aspects of the code they are planning to work on, to avoid duplication of effort.
Russ