I think i posted about member onboarding elsewhere. We're not currently recruiting volunteers, but might be something we're looking at in the future.
With clients the process follows one of three methods:
1) Headhunt skilled people. Find the people who have the most experience/skill/charisma to offer the community and gradually nurture them to take on real roles within the group through lots of flattery/impact.
2) Create roles and let people apply. Create specific roles that package up the good and bad things of volunteering. a lot of people just give volunteers the work they don't want to do. A good role should encompass the bad stuff like moderating/removing content, with the good stuff - such as creating content, managing groups etc. CMX does this pretty well.
3) Commitment consistency - similar to the first, but find people that have made a good contribution and ask them to take the next step on that commitment ladder - such as writing a guest column.
We don't usually have a system to automate it, but probably could with the right volunteers.