Which OS I use is really not an important factor when it comes to doing development work for me.. But, I feel more "at home" under a UNIX environment since I've done development soley on a solaris box for the 4 years that I spent in college. I happen to have both win2k AND linux at work on each of my boxes ( I have 2 ) ... I need to program in C , python, C++ ( only when programming COM stuff ) , and some ECMAscripting for web-related work, and what really matters is that I have the tools I need. After I tweaked the registry on my win2k so that tab completion works under CMD.EXE and installed unix utils I feel right at home even under my win2K box. Oh! Oh! Plus, Xemacs for windows has never been more solid in my opinion...

There's also the UWIN package from ATT lab. It seems to have a lot more apps and shells that come with it.. it even has gmake which I've used exclusively while I was at school. I might check this out some time...