I recently came across an article on 5-minute usability testing that also had a number of interesting links to other usability articles of interest. The idea behind the "5-minute usability test" (as I understood it) is to gather initial impressions that users have of your site - essentially a "gut reaction".
While not formal usability testing (and the authors of the article are the first to admit this), this kind of testing can provide valuable feedback in terms of the emotional connection your site may, or may not, be making with users. Since Web sites are essentially pieces of any organization's marketing, and lots about marketing (I am learning!) involves the emotional connection between the user and your "brand", this simple testing technique should perhaps be kept as one of the regularly used tools in the usability testing toolbox.