C++0x was the working name for C++11, but they are still the same thing. At this time, c++0x is tagged with 4 questions and c++11 is tagged with 98 questions. Although there's no problem retagging those 4 questions, it should still be okay to use either tag. C++11 just has the most questions because it's the final name of this standard.
This was already done on SO, so it should be correct. I cannot put in the vote myself since I don't have a sufficient tag score.