What do you mean by POSIX development ?
Yea well, I work for a .NET company and therefore I'm on windows on a daily basis.
It depends a lot on, what kind of development I'm doing, for example if I work in Visual Studio on some C# code everything is just fine, integration between SQL-Server/VS/ASP.NET-MVC is just great but when I have to work on web projects where npm is involved or commandline in general, it's a nightmare.
If found that the only useable shell on Windows is babun[0]. Executing Ruby or Python scripts is also not good at all and therefore I just use powershell for glue scripts.