The latest tool to come out of Google Labs will allow you to customize your search results through voting. The way this will work is that, when you do a Google search, you can then designate which results were most useful (thus, raising them higher in your search results next time) or tell Google that certain results were completely wrong (and hide them forever). A link at the bottom of the search results page allows you to completely undo your votes. You would need to be logged into a Google account in order to use this.

Google says that, right now, the system only works on a "per user" basis; that is, your votes don't influence Google's search results for other people. However, it's quite possible that Google might use this some time in the future to help their overall search engine ranking system, which would allow a person to vote his own websites up and his competitors down. Or, an even more likely scenario, search engine optimization companies would figure out ways to game the system, giving their clients millions of votes up and their clients' competitors million of votes down by running a computer script. It's likely that Google Labs doesn't yet allow the votes to influence all search results because of such potential for abuse.