Firefox beat Internet Explorer in number of people accessing wordpress.org by about 80,000 in January. Of the people visiting with IE, over 90% were using 6.0. This makes web development much, much easier.
Gigablast, the search engine run by one guy named Matt, allows you to do some interesting things with meta tags. Here is a search that finds all “generator” meta tags with “WordPress” and shows the tag itself in the search results. (About 1.5 million results.) I found out about this on the Gigablast blog which isn’t quite a blog. If Matt is looking for a better blog system, I have a suggestion. The results on Gigablast seem on par with Google’s for most things I tried, but the pages themselves need some UI and QA love.
Topix.net is built on flat files, not databases. My experience has been with the applications I do it’s easier to start with SQL and then cache to the filesystem/memcached.