Kelly Jackson Higgins in a Dark Reading article tells us that Malware Attacks Decline In SCADA, Industrial Control Systems, quoting a report published by the Security Incidents Organization drawing on its Repository of Industrial Security Incidents (RISI) database.
One aspect that's attracted attention on specialist lists is the mention of a large US power company that experienced infections of 43 operator and programming stations.
Added to the Stuxnet resources blog at /2011/01/23/stuxnet-information-and-resources-3/.
David Harley CITP FBCS CISSP
ESET Senior Research Fellow