LevelUp is a mentorship program that will start in January 2013 and that replaces the "20% time" policy https://www.mediawiki.org/wiki/Wikimedia_engineering_20%25_policy for Wikimedia Foundation engineers. Technical contributors, volunteer or staff, have the opportunity to participate; see https://www.mediawiki.org/wiki/Mentorship_programs/LevelUp for more details.
We started 20% time to ensure that Wikimedia Foundation engineers would spend at least 20% of each week on tasks that directly serve the Wikimedia developer and user community, including bug triage, code review, extension review, documentation, urgent bugfixes, and so on. It had various flaws. 1 day every week, I made people task-switch and it got in the way of their deadlines, and it was perceived as a chore that always needed doing.
It felt like enforcing a rota to do the dishes. So instead, let's build a dishwasher. :-) We can cross-train each other and fill in the empty rows on the maintainership table https://www.mediawiki.org/wiki/Developers/Maintainers so our whole community gains the capacity to get stuff done faster.
If you've been frustrated because of code review delays, I want you to sign up for LevelUp -- by March 2013 you could be a comaintainer of a codebase and be merging and improving other people's patchsets, which will give them more time and incentive to merge yours. :-)
When I asked what people wanted to learn, I got a variety of responses -- including "MediaWiki in general", "puppet", "networking", and "JS, PHP, HTML, CSS, SQL" -- all of which you can learn through LevelUp. When I asked how you wanted to learn, all of you said you wanted real-life, hands-on work with mentors who could answer your questions. Here you go. :-)
I won't be starting the matchmaking process in earnest till I come back from the Thanksgiving break on Monday, but I will reply to talk page messages and emails then. :-)