at http://drupal.org/node/73245#comment-115470 the suggestion came up to reuse the author field of the node table for linking users with usernodes.
Currently the usernode module uses its own table. The main reason why I decided to not use the author field is that I fear other modules, which might change node authorship.
quoting merlinofchaos:
If you're filling the author with that data anyway, I would highly recommend just telling Views that's the linkage. For one, it'll save a join, and for 2, anything which Views links to the user object via node author will work; otherwise, it'll be *very* confusing for people.yes, of course there is an additional join. but I'd like to have the difference to the node author. It wouldn't be clear to use node author information, if someone would list information of users. Imho that would be confusing. Imho straight forward would be if it's possible to select users's data (mail address, creation time..) directly as additional field. As it's the target to list users, not nodes with some author information.