Is there any hard data about the percentage of sites that use some kind of a CMS, as opposed to pure hand-coded HTML/CSS? From my anecdotal experience it really seems that more and more sites use a CMS nowadays, that hand coded sites take too long to set up, require too much time to maintain, are too hard to update regularly, etc. etc. Pure HTML sites seem insufficient for any but the most basic of websites.
Hand coded sites can be coded very quickly compared to having to make a design for a Content Management System this is because it's a lot simpler and each page can be altered separately without having to worry about breaking anything.
The main reason why CMS engines are used more than static sites isn't because the design process but the fact you can easily add content to them, from adding images, text, meta data and so forth, and because its on a CMS it updates the other pages IE if you have widgets and stuff.
To answer your question you can find out how many Websites use CMS here:
The above site also has lots of other data that you can use to learn a bit more about whos using what etc.
Furthermore for a approx figure of how many people are using the top CMS (Wordpress) Go here: http://en.wordpress.com/stats/