Marvel has created a wiki, called the Marvel Universe, letting fans contribute to the biographies of each character. There are thousands of characters, each one with an incredibly complex story behind him or her (or it), and it makes sense to leave the reporting to the people who know the history best and care the most: the fans.
I feel that for many of these fans, being able to contribute to the Marvel universe in this way is a reward for their support. In a way, it probably allows them to interact with their favorite authors, illustrators and (in a way) characters that isn't possible via the standard mailbag and conventions.
Official character bios are offered alongside the fan-created ones, proving that user generated content can peacefully coexist with corporate-sanctioned content. Similarly, each character has a bar graph representing their various skills (you know, real life ones like speed, strength and energy projection). For each attribute, there is the official Marvel statistic alongside fan-voted statistics.
In an ideal social media world, Marvel will be taking a look at what fans offer on these pages, and may even create wiki pages appealing to their fans for new content. For now, they've simply put together a great social media program.
I've never been a huge fan of comic books, although I do like the stories and characters. However, taking a look at the Marvel website and being reminded about the intricacies of the stories has inspired me to stop by a comic book shop sometime in the next few days and pick up one of those books collecting an entire story arc.
In short, their use of social media has created a new customer.
Well done, Marvel.