Amit Yoran, National Cyber Security Division Director, on the difference between the effects of the Mydoom virus versus past e-mail virus threats:

A few years ago, we experienced significant outages in our businesses from Love Letter and Melissa and other viruses. Today, even with a more sophisticated threat, the reports of outages [like networks going down, e-mail servers being shut down] is far below where it was a few years ago with those less-sophisticated viruses. The message here is that we have a lot of work to do but our overall preparedness is improving.
You can read more here.