The big problem with C++11 is that in g++ 4.6 (which is the one used in ubuntu 12.04 lts) it doesn't support this:
class a
{
int m_var = 0; //default value
};
And you have to manually write big constructor's initializer lists

Once I discovered this feature I am much more productive when writing new classes (it's so damn easier now). Unfortunately, it forced me to move to (L)ubuntu 13.04 so I have better C++11 support.
Why care about ubuntu? Well a majority of linux users use ubuntu and a majority of ubuntu users use LTS. However in april 2014 with ubuntu 14.04 lts the problem will be automatically fixed

The rest of C++11 features I use are available in g++ 4.6 so tgui 0.6 can still use many of c++11 (I'm yet to see modern distro with g++ 4.5 other than centos)
Tdm-gcc 4.7 is standard for Windows (shipped by codeblocks and codelite and generally widely-used) so no problem there.
And well, on those visual c++ users, I think we shouldn't care about them

It's better to force them to use open and better compilers, with better c++11 support.