This post over at BoingBoing describes how Meetup does usability testing: quick, dirty, and often. This is my ideal approach, too.
You see, I recently did a usability test here at SEP for an internal project. Unfortunately, I haven't had a lot of spare time to compile my results (either from the test itself or my upcoming report, "Why Usabilty Testing Is the Best Thing Ever, I Mean, Really"). But, because the test took on a similar form to Meetup's, my lack of "finished report" isn't that big a deal - the tool's developers observed the whole test and were taking notes the whole time. That, coupled with a few ten-minute "here's something you might not have noticed" discussions, gave the team enough feedback to fix (hopefully - I haven't seen the latest revision yet) a lot of the usability problems.
P.S. Because I haven't mentioned it before, if you're interested in the whys and wherefores of usability testing, you can do worse than to start with Steve Krug's Don't Make Me Think, which covers usability testing in brief, including instructions (which I took to heart) on how to do it for cheap.