There's a lot that does, though, and it's a huge set of functionality that windows doesn't provide natively. Even something as simple as:

     ipconfig | grep IP

Not possible in windows. Then there's the rest of the userland tools unix people take for granted like rsync, screen, diff, tr, wget, etc. The standard shells and scripting languages all work. Plus I always set up an ssh server to run on localhost, so that I can use putty as my terminal rather than the windows' crummy cmd.exe.

Yes, ultimately it's still a windows box and cygwin's distribution definitely isn't on par with ubuntu or fedora. It's not going to be cutting edge and there will be difficulties integrating with hardware and the windows environment. It's generally not a good choice for running desktop apps or servers, and will probably require some extra work to set up a serious development environment.

But if you have other reasons to use windows (Outlook calendar, games, etc.), cygwin makes it a LOT more tolerable.