From the "everything I ever learned about programming came from View Source" files:

Most search engines search for content. Opera's new MAMA search ("Metadata Analysis and Mining Application") is searching for what's behind the content. It's all about figuring out what websites are made of in terms of markup and technologies. Sure you can easily find that stuff out today without MAMA on a site by site basis (view source/page info etc) but looking at all that info in the aggregate as a search is something that I personally have not seen in the way that MAMA provides.

"Say you want to find a sampling of Web pages that have more than 100 hyperlinks or for pages that use the Font-size CSS property that also use the FONT element with a Size attribute? Many parties would be interested in such a service, even if the market would be smaller than for a "traditional" search engine," Opera's Brian Wilson wrote. "For browser makers and standards bodies, the structure and composition of the Web is a more pressing issue than its content."

Beyond just being a search tool, Opera has also already done some aggregate analysis based on an initial analysis of 3.6 million URLs. Among MAMA's findings is that the open source Apache Server dominates with nearly 68 percent as compared to Microsoft's IIS which had a 26 percent share.

Flash is also represented though the penetration is less that I might have guessed. According to Opera, the total number of MAMA URLs using the Flash plugin is 1,176,227 (33.5 percent).

AJAX relies on XHR (XMLHttpRequest) so I would have expected to see it heavily represented as well. Opera reported however that XHR was used in 112,277 of MAMA's URLs 3.20 percent  of all its Web pages.

The only other stat from MAMA that if found a tad surprising was the CSS (Cascading Style Sheets) penetration. Opera reported that they found CSS iin 2,821,141 MAMA URLs 80.39 percent. I guess the other 20 percent are still using <table>.

Overall, this is definately a valuable tool for looking at broad trends. But I'd caution individual site owners/developers to always place more faith in their own log file analysis as experience has taught me that individual experiences always vary.