As far as development tools, they're overwhelmingly Windows based.
The majority of Xilinx' tools are available in Linux versions. I actually really prefer the Linux versions as using them from command line is far easier under Linux than under Windows (provided you want to script your process instead of using the GUI, probably not as useful for someone just getting started). Also, AFAIK, the larger Xilinx FPGAs require the *nix tools for a guaranteed Map/PAR due to memory limits, etc. You can use the Win32 version, but once utilization gets high enough, the Win32 versions may not be able to completely PAR the design.