I have been in the computer security auditing and remediation business for banks, municipalities, etc. since the late 80's.

Blast is correct. Hacking the power grid or just about any other public utility is a potential threat. If it is connected to the Internet, it is potentially at risk. Also, it doesn't take much for an insider to compromise even the most sophisticated security system.

However, as an individual, I would be more concerned about ever growing number of ways that you can have your identity stolen.

For example, we had a local fast food worker stealing debit card numbers using a hand-held card reader(skimmer). This is a fast growing problem, because it is so easy to do.

http://www.suburbanchicagonews.com/heraldnews/news/716130,4_1_JO28_CARDSWIPE_S1.article

GarlyDog, CISSP