According to a study made by Metadata Analysis and Mining Application (MAMA), a tool created by Opera that crawls the web and indexes the markup and scripting data from approximately 3.5 million pages.
Some of the most relevant parts of the study are:
• About 35% of all web sites use Adobe Flash.
• XMLHttpRequest (AJAX) scripting mechanism is used by only 3.2%
• CSS is used in the 80% of the web sites.
• Using the W3C validation tools, shows that 4.13% are valid, which only 50% using the validation badge are valid.
Read the complete article at arstechnica.com