I've long wanted to build a search engine of only personal blogs. I am less familiar with the field of information retrieval so I haven't gotten started yet, but it's always been a dream of mine and if anyone is interested please contact me at threemillionthflower [at] the world's largest email provider.
Discovering unknown parts and blogs on the internet is one of the enduring goals of a newsletter that I run [1], which provides a single link to an interesting article every day, usually by lesser-known authors and blogs across the internet.
[1] www.thinking-about-things.com