On first read (via an email), I was a little frustrated with the article as it all seemed so anecdotal and based on opinion. But I persevered as it tied in with what Jakob Nielsen had summarised late last year.
Gerry's website version of his article also includes a link to a whole wealth of back up research courtesy of Tom Tullis of measuringux.com. This presentation is well worth a read in its own right - the pertinent slides on imagery are 20 to 25.
Are marketing images damaging your website? - article by Gerry McGovern