In December 2005, Google did an analysis of a sample of slightly over a billion documents, extracting information about popular class names, elements, attributes, and related metadata. The results are now available – and very interesting:

It seems most pages use presentational attributes: the fourth most used attribute across all elements is the table element’s border attribute, followed by the height and width attributes on img, followed by <table width="">, <table cellspacing="">, <img border="">, and <table cellpadding="">. Interestingly, though, the most frequently used attribute on the body element (namely bgcolor) is only used on around half of pages, with all the other presentational attributes on body being used even less. One possible explanation is that on average, colors are mostly done using CSS, while layout is mostly done using HTML tables.

Web Authoring stats – Elements and attributes