I think C++11 is preemptive; it isn't standard yet, after all. So until then, it should keep its colloquial name.
That said, we still have the question: When C++11 is official (or C++12 or whatever), should we change the tag, and if so, when? I think it's clear that the name should be changed eventually, so I'll omit that discussion, and focus on when.
I think even after it's been out for a long time, people will still refer to it as C++0x, especially people who don't keep particular close track of the language standard (most people). Therefore, I think it would be best left at C++0x for some time after the standard is released. When people stop tagging it as C++0x but instead as C++11, consistently, then we can change it to C++11.
Note, though, that you and I now both refer to the current standard, C++03, as just C++ (ignoring cases where we explicitly state the year, for emphatic reasons). We refer to the old standard by year, C++98, and the future one by codename, C++0x. In the future we'll refer to C++0x/C++11 as just C++, and the current standard, then old, as C++03.
What I mean to imply here is that when the time comes, we should not have a C++0x or C++11 tag at all for C++ questions, because that'll be implicit. Questions that need answering with only the support for the old standard will be tagged C++03.
The crux of the issue, then, is that these two things are going to happen at simultaneously: we'll start to see less usage of C++0x and more usage of C++11, while the explicit use of C++0x/C++11 will vanish anyway. How can we cope with both at once? I have no idea. I say wing it.