hackday.org has the signup details for this Hack Day at Yahoo which include a weekend festival of tents, tunes and TechCrunch Michael Arrington presiding. via Techcrunch:

On Friday, September 29, 2006, Yahoo will open up its Sunnyvale headquarters to all developers for a 24 hour Hack Day, followed by a really cool party on Saturday night. If you are a developer, and have an idea for a cool one-day hack project, this will definitely be a fun event for you.

Will be looking forward to see what cool things come out of:

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Gotta love the final taunting line: “Mashup or shutup!”