If you decide to go with a mad-libs form, you'll probably want to do some testing of your own. Patrick McKenzie of Bingo Card Creator tested a mad-libs form against a standard form, and found that the standard form was more effective ( http://www.kalzumeus.com/2010/02... ).
Ufuk Kayserilioglu, A physics PhD turned veteran polyglot software developer
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There is also OpenChime (http://www.openchime.com/) which uses mad-lib style forms for initiating user requests. In my personal opinion, they get much better user experience by the use of mad-lib style forms coupled with multi-step, funnel forms (with a little machine smarts attached).
While the huffduffer sign up is by far the most well known, I would argue that the best implementation that I've seen is The Bureau of Communication. Mad Lib style forms seem to do best when there is a genuine narrative flow. Their forms have this flow and capture the nostalgia of filling out paper forms for crazy things.