Why didn't anybody tell me?
According to TomPaine.com, the FBI is circulating a memo warning corporate America to expect violent attacks from anti-war protesters the week of December 15-21 (see article here).
The article suggests that this is not so much a serious warning about a realistic threat, but a cheap attempt to discredit the anti-war movement just when it's building up steam. Forty percent of Americans are now questioning the need to go to war against Iraq, and that's got the folks in DC scared.
I agree that it must be mere propaganda, and not a realistic threat. After all, nobody told me to start making Molotov cocktails. If the FBI memo is real, then somebody's taken me off the anti-war mailing lists.