I wrote a little crawler which counts the number of WordPress blogs (among others such as blogger, .Text, BlogTool etc) that ping weblogs.com and Blogrolling.com recently updated list. Here is the link to the most updated stats. The crawler has just been running for a day and if your site is not in the list, please be patient and it will get listed in time. The crawler code is being tested and modified and the database might get emptied from time to time for code changes. However, it looks good for now and is a very good place to advertise the variety of sites that WordPress can handle. I am planning to add an XFN crawler when I get the chance. I will make the database available publicly (after you promise to NOT use it for nefarious purposes) once it reaches a 100,000 entries. Please let me know what you think.
PS: Please do not remove or modify the generator tag that exists on the top of the WordPress index.php Thats what is used to identify WordPress blogs.
PPS: I am looking for a good way to identify MT blogs. I realize that there are no meta tags which do so at this time. If you know of anything, please leave a comment or email me. Thanks!