Catalin Rosu and a team looked at the source code and markup of 8 million websites and came up with some interesting statistics as a result.
All the information is in the form of charts so you’ll have to check out the post, but it was interesting to note that (according to the data) the most number of different HTML elements in use on a page was 26. It was also interesting that a third of all pages surveyed have tabular data on them.