Amen is much simpler than writing out a review or choosing a star rating like most other user-generated recommendation services. It’s kind of like Mad Libs.

So, for instance, Ashton Kutcher — an investor in Amen — recently posted “‘American Movie’ is the best documentary ever,” and “Led Zeppelin is the best rock band ever.” If other users agree with Kutcher’s proclamations, they can post “Amen.” If they don’t, they can post “Hell no!” and nominate something else that better fits the description.

These statements may seem silly — and indeed many early Amen users seem to be using the format to joke around — but they might just be tremendously useful, said Amen co-founder Felix Petersen.

That’s because Amen is generating structured data, the elusive building block of the semantic Web that so many companies would love to capture. And it seems to be somewhat addictive. In a month of beta testing, 3,000 users have created 30,000 statements and 80,000 Amens, Petersen said.

Petersen hopes these silly little statements could turn into something big, because Amen understands both how to classify what a user is talking about and how statements relate to each other. Amen already generates lists within each category, ranking which response got the most Amens.

Soon, the company plans to release its lists as Web pages to be indexed by search engines. (Everything posted on Amen is public.) Eventually, advertisers will be able to purchase sponsored placement within the lists, similar to AdWords, Petersen said.

Amen is based in Berlin and was co-founded by (extremely) early Twitter engineer Florian Weber and Petersen, who previously co-founded Plazes, which was sold to Nokia.

Petersen said he and Weber started out with the idea of building a service to help users generate free-form lists, but realized that they might get more participation if they made it easier and more fun to contribute.

Amen has raised a bit of funding from Index Ventures, in addition to Kutcher. The company has built both a Web site and an iOS app, and plans to let in waves of people as they sign up, Petersen said.

This morning Nokia (NOK) acquired location-based services venture Plazes, which has developed a sort of social GPS that allows users to tell one another where they are and what they’re doing. For Nokia, the acquisition is a way to add the elements of place and time to its Mosh social network. And for Plazes, which has no business model of which to speak, it’s a quick and easy way to get one.

“If all goes well, in the near future Plazes will be made available to millions of Nokia customers both online and on millions of mobile devices,” Plazes CEO Felix Petersen said in a post on the company’s blog. “Nokia is a perfect partner for us because they share our product vision and have the muscle to bring locative presence to hundreds of millions of people all over the world.”

Presumably the “They were actually willing to buy us” is implied.