I haven't had a lot of time to think this through the major possibilities, but it seems like it would be better to promote the asking of good questions (that receive up votes) and right answers (that receive up votes and/or acceptance) rather than just asking/answering 10 questions.
I'm thinking that a pure reputation score wouldn't work, but perhaps something like 3-5 questions/answers and 250 reputation to meet commitment. Or perhaps a scaling where n rep or m postings are equivalent to x "points" and you need y points to meet your commitment - a single really awesome question or answer might be fulfillment, but a larger number of OK or good questions/answers might be needed.
I'm also thinking about other, non-question/answer activity perhaps counting toward commitment. Upvoting, downvoting, commenting, getting upvotes on your comments, and participating on Meta to help define the community might be other ways that commitment to the community can be fulfilled.
Thoughts? Something I'm overlooking?