I did a small comparative analysis of markup practices at several major search engines. It’s interesting to note that only one engine is using valid markup and CSS layouts, and that would be MSN. Close behind is AOL, whose validation problems are mostly related to ampersands not being escaped, and HotBot, who have a few easily corrected errors.
A very interesting comparison of the code used on a wide variety of common web search sites. Surprisingly MSN Search is by far the best and actually is the only site to validate as valid XHTML.
Wandering the Interwebs 