Symantec commissioned a survey at the recent Black Hat USA conference in Vegas. The results are in and reveal that "Web 2.0" technologies (e.g. sites that rely heavily on Javascript and Ajax) and virtualization are the two main concerns for those security-minded administrators who responded to the survey.
The results, which include many more interesting anecdotes, were posted to the company's Security Response blog a couple of weeks ago. So in case you didn't read it already, head over and have a look.