I just happened to be exposed to the question of creative commons license compatibility in a couple of different contexts. It isn’t entirely trivial, but anyone who has done meaningful research into licensing will know, that overall copyright law and resulting licensing requirements are complex, tedious and mostly still highly jurisdictional (country by country differences), to say the least.
The Creative Commons licensing approach has been of immeasurable help to give non-lawyers a fighting chance to share and license some of their works without having to give up all ownership control over those works. Another huge benefit of standardizing some licenses, is the possibility to create derivative works, remixes and mashups, which would be otherwise entirely impractical, because every derived work author would have to contact and strike individual deals with every individual owner (or license management organization) of a previous generation work, which has been used to create the new work.
However the Creative Commons licensing approach deals (at least so far) only with non commercial licensing. This is still a very big deal, because it allows sharing, dissemination, remixing in non-commercial contexts.
But still, not all creative commons licenses are compatible – simply speaking that is, because the owners of the works using the licenses have different objectives in mind. Wishing that away is in my opinion a bit naive or a bit too militant, so I’m not one to advocate total uniformity in licensing. That would be as bad as total uniformity in languages, dress, operating systems, search engines or blogs 🙂
So for those who are remixing, deriving and mashing up like I do, generally with creative commons licensed materials, here is a key page you will want to bookmark: A creativecommons.org blog entry pointing to two CC license compatibility charts. One is an interactive tool from the CC in Taiwan, the other is a text link to a chart in the creative commons FAQ.