I would encourage any dev / bot owner fluent enough in python to give a try to the rewrite, particularly if you use scripts fetching a lot of data from mediawiki.
I wrote for example, a maintenance script for the French translation project. It fetches hundreds of pages, does some mambo jumbo magic on it, and eventually use that data to update ~200 summary pages.
I first wrote it using our trunk pywikipedia. (since editing through the api is not yet available, I first thought that it was the only way). It was very, very *slow*. I wondered what improvements I would get using the rewrite, and I rewrote my script to use the rewrite for all the page fetching part. Well, I don't have precise figures, but I would say that the latter version was probably 3 to 10 times faster
In addition to being faster, the more we'll use the rewrite, the more we'll be able to detect bugs and to correct them, the easier it will be to merge the branch when API editing will get available.
(Speaking of debugging, if you're being annoyed by the debug output while writing your scripts, import logging ; logging.getLogger().setLevel(logging.INFO) in your script header will help. )