Although timethief has offered some Google tips to search Word Press blogs, alot of people don't want to memorize search string syntax to type in search statement..which librarians, serious researchers and maybe some computer folks might undertake. Part of the problem people is don't want to memorize specific search syntax /commands because different search engines have different search syntax requirements. Heck, most people are trying to remember multiple passwords for work, personal stuff.
What would be helpful is wordpress.com & wordpress.org provide the option for blog developer to define field specifc search boxes...for Title, Author, Tag/Category and Year to narrow the search parameter. Like what one sees in a mega-library database.
Now, doesn't that sound like a relational database structure? :)
The date range search limiters would be helpful to filter extraneous search result hits,since blog content in blogsphere continues to mushroom. ie. search for xxxxx between 20007 -2010 or anything before/after 2008.
Until WP develops this basic search engine flexibility (and please not just drop down menus from search selection boxes), it's tough for WP to claim content management software capabilities on par with much more robust content management software ie. Oracle, LiveLink, etc. which are for huge, complex business needs or for complex data management.