I'm especially interested in tasks where there's a lot of work to do -- that way, people can be given lots of hands-on things to do that can provide practice to help people be more comfortable with tools like git and gerrit, or more comfortable with the MediaWiki hooks, or where the task gives people a reason to install MediaWiki on their own machine. Additionally, it's important the task meaningfully contributes to the project, so people feel the value of what they're doing.
It's also a good opportunity for people to get familiar with Labs, and maybe help out with a current project that does something MediaWiki related.
I expect that we'll get a lot of people with some PHP experience but who have little experience with, say, Git and Gerrit.
Getting enough of the basics of Git/Gerrit to push in code is easy enough that people can really focus more on coding.
Also, if you'll be at the Wikimania DC 2012 Hackathon and want to help mentor people through any of these, reply as well.
Other ideas welcome. I'll be collating these over the next few days, and then trying to pick the ones with the highest probable impact based on the attendees. One warning: this is intended just as a research question for now. I can't promise that I'll focus a portion of the hackathon on your particular suggestion. But I do aim to stay in touch as the planning progresses.
Don't forget about opportunities for volunteer operations work as well. People don't necessarily need to hack on MediaWiki. If they want to fix operations things, that's doable as well.
- Ryan