As for windows support, I should say that it's really just as good as the gnu toolchain support is on windows. There is no support for using Microsoft's toolchain on Windows. It can also take some work to make go apps not run within cmd terminal. I saw a blog post about it recently but I can't find it right now. But it also mentions things like the syscall[3] library docs on golang.org are actually for Linux, and it takes some steps to get them for other platforms, see the header comment here[4].
So Windows support is pretty good, but it is definitely not Google's focus. But if you've ever heard about what Windows is like within Google, there is a good reason for that.
[0] https://groups.google.com/forum/#!topic/golang-nuts/YG-APRPw...
[1] https://groups.google.com/forum/#!msg/golang-nuts/DS5ZGswXC6...
[2]https://code.google.com/p/go/issues/list?can=2&q=label%3AGDB
I wouldn't imagine writing a GUI app in Go, Go just isn't made for that and it would be silly since Microsoft's .NET tooling is so darn good. But Go for services and command line apps for Windows it has been fantastic.
That said, I still use Go all the time.
[0] http://www.abtinforouzandeh.com/2012/04/08/Do-Not-Use-Go-For...
EDIT: For the record, I'm using it on Windows