You might find some good information paging through the last year or so of the A Photo Editor blog
. He has some interviews with art buyers and others at ad agencies. You also might find it useful to spend a few dollars talking with a consultant about your approach -- there are several former art buyers doing this now.
For example, this thread has some good info:http://www.aphotoeditor.com/2010/06/03/ask...93-the-meeting/