In spite of the (justified) complains you get about the false positives, I think that's a great way to go. Unlike with email where missing a message might be critical, in search I'd rather have even as much as 10-20% false positives than deal with the spam sites Google delivers.

More in general, concerning the front page search examples: "cure for headaches" works very well indeed compared to google. However, "global warming /liberal" is a bit irritating. I understand the rationale behind it, however there is this slight difference between finding only what one is looking for and hearing only what one wants to hear. To find anything non-mainstream might necessitate a technique like this in Google where you otherwise don't see anything else in the first 50 results... But maybe you can strive to find for me what's really going on and not merely what's mainstream and politically correct. Thinking about it, your blocking of domains like Answer.com might be a great step in that direction anyway.