There's a problem with how the Stack Exchange terms of service are phrased. Currently, they include the following paragraph:
In the event that You post or otherwise use Subscriber Content outside of the Network or Services, whether such Subscriber Content was created by You or others, You agree that You will follow the attribution rules of the Creative Commons Attribution Share Alike license as follows:
If interpreted literally, it says that if you use Subscriber Content (i.e., material contributed by users, such as MO questions and answers) anywhere else, then you must follow the attribution rules of the CC BY-SA license, regardless of whether the content is also available under another license. In particular, it specifically says this applies to your own contributions, and it seemingly forbids you to re-use them elsewhere without following the CC BY-SA attribution rules (although, as the copyright owner, you would normally be free to ignore these rules).
The wording is a little ambiguous, so this may not be the only possible interpretation, but it's certainly not clear that it means anything else.
This came up before, and the outcome was that the literal interpretation is not what Stack Exchange intends. Specifically, they provided a link to this answer, which says that you can do whatever you want with your own contributions (release them under a different license in addition to the CC BY-SA license, put them in the public domain, etc.).
Everyone seems to be in agreement about what should be allowed, but the terms of service should be fixed to reflect this consensus. Right now, they are unclear or misleading, and that is itself a problem even if nobody intends to enforce a literal interpretation.
I'm of course not a lawyer, so my phrasing should not be used without confirmation that it means what I think it does, but I'd propose replacing the paragraph quoted above with this one:
In the event that You post or otherwise use Subscriber Content outside of the Network or Services under the terms of the Creative Commons Attribution Share Alike license, You agree that You will follow the attribution rules of that license as follows:
In other words, the terms of service should specify the attribution rules for the CC BY-SA license, without ruling out the possibility that re-using content might sometimes be allowed on other grounds as well.