I’ve seen a lot of ham-handed Facebook marketing of late but it looks like the folks over at Guinness have a solid idea of how Facebook works. They’ve been using it — and other social networking services — to encourage people to sign their petition asking that St. Patrick’s Day be declared a national holiday. The Facebook group they’ve started has over 15,000 members as of this posting.

This campaign is innovative because it leverages the already existent “activist” behavior on the social Web to promote a product. For example, Facebook users routinely join groups to support the causes they care about. Often at times, that’s the extent of their “activism.”

But for a social marketer with a real cause to shout about, maybe we should take another look at facebook . . ?