I was talking to Cynthia Kurtz once and she mentioned, "If I were developing a piece of software I would always want to put a Eureka Button on every page."
A Eureka button is this: if while using the system a user just figured something out that others might benefit from, he/she would click the button and be presented with a page where she could enter:
Where does this apply?
When should people read this story?
This input and information about where they were in the system (page & data) would be uploaded to a database. The database can be searched for patterns or browsed periodically, looking for bugs or unexpected uses of the system.
It's easiest for me to think about the Eureka Button in the context of enterprise software. Having worked a lot with CRM systems for telephony, I know that these systems have hundreds of user pages, with a virtually infinite number of paths through the system.
In these environments, product managers may know in theory how people should use the system. But their knowledge is quickly overtaken by experienced users, who learn how to apply the system to their jobs, often finding tricks or shortcuts to make the system work better for them. ("Eureka! I just figured out that if I dummy out some data items, I can capture information & save information from a prospect before they decide to make a product purchase. If they call back, I can look them up by their phone # and I don't have to start all over again.")
In this situation, a Eureka Button has great value for the product manager and the users. Product managers can learn about difficulties users have and how they overcome them. The tricks can be incorporated into the product, or deficiencies addressed. Users can learn from each other--perhaps Eureka Button entries can be blogged automatically and read by other users, dispersing tips and tricks and encouraging others to share their stories.
I can't even begin to catalog how a Eureka Button could benefit consumer sites, where (especially recent) products follow an emergent, iterative development approach and patterns of usage can affect the entire purpose of the product (e.g., Twitter). There are people much better suited than I to discuss some of these implications. If you're one of them, please let us know in the comments how the Eureka button could be used with these products.
(In searching for prior references to a "Eureka Button," I discovered this NY Times article from 2004. The article mentions that "'It's amazing how many people there are who find pleasure in sharing the little discoveries they make.'" The article focuses on undocumented features in PC software and in consumer electronics. The article references a site that publishes user stories of hidden Windows features.)