However, there is a new version of the MinGW toolset which includes a shiny new version of gcc (v4.4). By all accounts this is a much faster compiler that generates better code. This toolset will hopefully ship with Qt 4.6.
Although MSVC is a superb compiler, I don't want to have to depend on it, so I look forward to gcc 4.4. Having versions of Qt built with different compilers is an interesting exercise for the user but is ultimately a pain in the arse to manage.
Note that disabling support for exception handling can mean smaller executables when building with gcc, but I haven't tried this and am not sure how I can specify the relevant compiler options from Qt Creator itself.