See attached screenshots,
I've added a vs2010-x64 Qt build in Qt Creator, and Qt Creator correctly detects my VS toolchains. However when building it uses the x86 compiler and linker, as if it ran "vcavarsall.bat x86" regardless of the toolchain.
Same setup works fine with Qt Creator 2.4.1
Seems like the mirroring bug for https://bugreports.qt-project.org/browse/QTCREATORBUG-7180