Awhile back, Google acquired Kaltix. Now Google Labs has launched Google Personalized Search, which adjusts your search results based on a profile that you fill out. Each profile consists of a bunch of categories/subcategories that you indicate that you're interested in (there's even a checkbox for birding).
The actual search is the cool part (it also makes me pretty sure this is Kaltix). When you do the search there is a slider bar that lets you select how personalized the search is. It starts off at "min," but as you slide it, the results instantly change to reflect your profile. I tested this with "armstrong." The top search result was "Armstrong Floor, Ceilings." When I started moving the slider, Lance Armstrong and Neil Armstrong moved to the top of the search results (I had checked "cycling" and "astronomy"). I was disappointed to see Satchmo drop from the results, so I went back and clicked "jazz" and Louis Armstrong stayed in the top search results.
The one question I have with this approach, though, is whether or not a high-level, explicitly declared profile is actually going to get the search results people want. I think one of the canonical examples for personalized search is searching for "Java." There's plenty of checkboxes for computing-related interests, but I don't see any for "Indonesia" or "Coffee" that might help out people who don't want results related to the Java programming language. At the same time, if there were checkboxes for topics as specific as "coffee," it might make filling a profile out a bit overwhelming. Perhaps, instead, there needs to be a ternary state to the high-level checkboxes: not specified, interested, NOT interested.