I really enjoyed this "WebSpam" (link is correct, talk is mislabeled on Google Video) talk by Marc Najork from Microsoft Research.
It covers a lot of the techniques for web spam, examples of their tricks, spammer's motivations, and some of the countermeasures. Light and fun. Slides from the talk (PDF) are also available.
This talk is from Marti Hearst's SIMS 141 Fall 2005 class at UC Berkeley. There are slides and videos from many other talks available on that page. She had a remarkable set of speakers that included Jan Pedersen, Daniel Rose, Susan Dumais, Peter Norvig, Sep Kamvar, Bradley Horowitz, John Battelle, and Sergey Brin.
The quality of the videos on the SIMS 141 course page is low. There are higher quality videos for some of the talks on Google Video. A few of these talks on Google Video appear to be mislabeled; look at the comments at the bottom of the page to get the right titles.
Of the other talks, I particularly enjoyed "User Experience Issues in Web Search" by Daniel Rose from Yahoo Search. Peter Norvig's talk was also a lot of fun, but the low quality of the video available from the SIMS 141 page keeps me from recommending it. Finally, if you haven't looked at the Stuff I've Seen desktop search project from Microsoft Research, definitely look over the slides (PDF) from Susan Dumais' talk.
Unfortunately, Sep Kamvar's SIMS 141 talk on search personalization at Google appears to have not been recorded. Darn. I very much would have liked to see that.
Marc Najork also was at SIGIR AIRWeb 2006. I wrote up some notes on one particularly interesting discussion that involved Marc and many others. I also have other notes on the short presentation I did at that workshop.
On the Stuff I've Seen project at Microsoft Research, please also see some of my previous posts on that project, including "Using the desktop to improve search", "Finding and discovering", and Google Memex".
Thanks to Nathan Weinberg for reminding me to go back to the SIMS 141 page and mentioning the Google Video versions of some of the talks. Thanks to Danny Sullivan for originally pointing out the videos and slides available from the SIMS 141 page. And, thank you, Professor Marti Hearst, for making this remarkable content from your class available to all of us.
Update: The titles on the copies of the talks on Google Video have been fixed. They are now all correct.