Google's blog just published some info about Unicode use on the web. Unicode nearing 50% of the web . By Mark Davis, Senior International Software Architect. @ googleblog.blogspot.com…
Here's their graph:
Note that Unicode is also the standard charset in many computer languages. For example, Java 〔☛ Java Tutorial: Unicode in Java〕, HTML4/HTML5/XML/CSS 〔☛ Character Sets and Encoding in HTML〕, python 3 〔☛ Unicode in Python〕.
For popularity of other web stats, such as wiki engine, js library, cms, see: Web Tech Stats 2010.