I don't mean 13.04 in particular, I mean Ubuntu in general (though 13.04 does come with some nice UI updates). Before I became a developer, I used Windows. When I started trying to get into more serious development, trying to do it in Windows was just awful. Ubuntu was a breath of fresh air. From an interaction standpoint, minor things like workspaces, always-on-top, etc are great for my workflow. Things often take more work to get up and running due to various issues like hardware incompatibility or lack of software support, but once you do get it running I feel like it's smoother and more stable than Windows. Software management (e.g. installing and removing packages, adding and installing from various sources, updating) is more logical and consistent than for Windows (e.g. downloading and installing executable, managing updates individually).

This is all subjective and I wouldn't consider myself an expert on either OS so I could be wrong on some accounts, but that has been my experience.