While working on the current website of Radio Študent, I wanted a node to have multiple authors, because many of the published articles were collaborations of multiple writers. I presumed Drupal would support this out of the box, since it seems like a relatively common situation, but it didn't. So here's how you can do it manually.
Having references to all authors on the node is cool, but we also need to show all nodes of a single author on his profile page, whether he's the main author or just entered among additional authors in our new field.
I admit it's not the cleanest thing ever, especially with the patch requiring manual reapplication whenever Views are updated, but it seems to work well.
I was given a possible alternative solution when I posted this problem on Stack Overflow. It sounds even more promising, though I didn't use it at the time, because I had issues with Rules (ongoing problem since my childhood).