As far as finding useful information, I primarily used Blogline's Search Tool. I typed in a keyword and more often than not found useful feeds to add to my Blogline. I did have some trouble with certain sites that initially were listed as having an RSS feed, but as I tried to add them to my Blogline account I was informed that the particular site does not provide an RSS feed. I had to dismiss a handful of potentially useful blogs because of this. I am not exactly sure why they were included in the initial search retrieval because I was certain to select only those blogs with RSS feeds (I am paraphrasing here - I can't remember the exact terminology).
I used Feedster as well, although a lot of information that I retrieved using this search tool did not seem to be very useful to meeting my objectives. While using Feedster, I located several feeds that were not entirely relevant to the initial search goals.