Since building my own Joomla template framework I won't have much use css2switch, but this well-built extension helped me out a couple of times when all other customization options had failed. Much easier than managing multiple templates, especially if one only needs to change a few small but perhaps important structural details to particular pages. It's dead quick to slice through thorny layout issues on especially customized sites, or templates converted from client designs/HTML. I'm sure there are many other uses for the creative template designer/developer and this is a handy, easy to use tool.
My only caveats. It's 'branded' —so if you like your HTML output to be clean and free of other developer's URLs and comments you're going to need to get into the code to redact all that. In that sense, it's a kludge: a brute force method of making your CSS work on Joomla. It's also a lot of configuration and it's yet another extension to manage if all you're trying to do is some simple unique page styling; make sure you can't accomplish what you need with template overrides, using the Page Class Suffix, or some other method of granular CSS control-by-page. Finally, I don't know if this will be ported to 1.6 and beyond but due to improvements in the core of Joomla's template engine it seems that a strong designer/developer wouldn't even need something such as this.
But as it stands, for Joomla 1.5., this is a fast way for a HTML/CSS developer to get designs Joomla ready without having to get into a lot of the deeper Joomla customization that can be intimidating.