A useful article on the pros and cons of eyetracking, from a London-based usability company. They're obviously selling their service, but it's an upfront and worthwhile appraisal.
Eye tracking: Eye candy vs. I can do - an article from webcredible.com
Webcredible also wrote an article on the downturn in demand for eyetracking studies they've experienced in 2009. Again, an interesting appraisal of why this might be, plus a bit of video footage of an eyetracking session which may be of interest if you've never seen this kind of thing before.
Eye tracking - A short-sighted future? - an article from webcredible.com
Webcredible - user experience research and design company