Technical commitment: Ten questions/answers, particularly in private beta. Commitments expire after three months of beta so after 3 months if you didn't ask or answer ten questions you can no longer fulfil your commitment. This answer is based on having been through more than one beta in the past.
Note that commitments cannot be deemed filled until after the site has been in public beta for about a day. Sites that fail in private beta (I don't think us!) will never register fulfilled commitments.
Community commitment: As Stephan says, it is about building the site. This is more open-ended. After the site goes public, it's easier for people who want out to just leave and we can hope that new people come in to fill the ranks and help make the site better.