I currently develop in C++ on Windows, using Visual Studio 2010. After the official announcement of C++11, I have begun to use some of its features that are already available in
GCC's C++11 support is quite phenomenal (and quite up to par with standards conformance, now that <regex>
has been implemented).
If you replace your compiler, you'll need to make sure every dependency can be built with that new compiler. They're not made to be substitutable plugins (although Clang is working on becoming that way).
GCC is a fine compiler, and can produce code that has pretty much the same performance, if not better, than MSVC. It is missing some low-level Windows-specific features though.
Apart from this, to answer your questions:
I my humble opinion, it's depends how someone started to code in the first place. I've been using g++ and gcc for more than 20 years now but the reason why i keep using gcc is mainly for licensing reasons. Although i like it too when i don't have a bunch of runtime dependencies or dll's to bundle with my stuff since i came from the DOS era, i still like my stuff small and fast. gcc for windows comes with standard win32 libraries and common control but i had to develop my own win32 controls for stuff that might require mcf shit to work properly or just to look nicer.
Although gcc might have strong support over internet, when it comes to win32 stuff, many rely on mcf and vc proprietary stuff so again, one may have to work his own issues around and be creative when difficulty arises.
I think it's all about needs and circumstances. If you are just a hobbyist coders and have the time for researches, creating you own libs and stuff but you want a solid compiler that's around since the late 80's and free, gcc sound perfect for the job.
But in the industry visual studio is a must if you want to be competitive and stay in the race. Many hardware manufacturers would prefer bundling visual studio compatible libraries for they hardware over some opensource gnu stuff.
That's my two cents.
MSVC has the huge advantage of coming with an IDE that has no equals under Windows, including debugger support.
The probably best alternative for MinGW would be Code::Blocks, but there are worlds in between, especially regarding code completion and the debugger.
Also, MSVC lets you use some proprietary Microsoft stuff (MFC, ATL, and possibly others) that MinGW has no support for, and makes using GDI+ and DirectX easier and more straightforward (though it is possible to do both with MinGW).
Cygwin, as mentioned in another post, will have extra dependencies and possible license issues (the dependency is GPL, so your programs must be, too). MinGW does not have any such dependency or issue.
MinGW also compiles significantly slower than MSVC (though precompiled headers help a little).
Despite all that, GCC/MinGW is an entirely reliable quality compiler, which in my opinion outperforms any to date available version of MSVC in terms of quality of generated code.
This is somewhat less pronounced with the most recent versions of MSVC, but still visible. Especially for anything related to SSE, intrinsics, and inline assembly, GCC has been totally anihilating MSVC ever since (though they're slowly catching up).
Standards compliance is a lot better in GCC too, which can be a double-edged sword (because it can mean that some of your code won't compile on the more conforming compiler!), as is C++11 support.
MinGW optionally also supports DW2 exceptions, which are totally incompatible with the "normal" flavour and take more space in the executable, but on the positive side are "practically zero cost" in runtime.
It can't be used as a direct swap-out replacement for the microsoft compilers, for a start it has a vastly different set of command line arguments and compiler specific options.
You can make use of MinGW or Cygwin to write software but introduce extra dependencies ( especially in the case of cygwin ).
One not often touted advantage of gcc over cl is that gcc can be used with ccache to drastically speed up rebuilds or distcc to build using several other machines as compiler slaves.
GCC and MSVC use different name mangling conventions for C++. C++ dlls compiled by one compiler can not be used in applications compiled with the other. I believe this is the main reason we don't see more widespread use of gcc in windows.
Consider the Intel compiler (or "Composer" as they seem to have taken to calling it) as another option. I'm not too sure where its C++11 support is at compared with MS (certainly it has lambdas), but it does integrate very nicely with VisualStudio (e.g different projects within a solution can use the Intel or MS compilers) and there's also been some efforts made to match the MS compiler commandline options.