According to the National Counter Terrorism Center (NCTC) and Duke University 2011 was a blissfully domestic attack free year here in the U.S. Duke Classified one Islamic terrorist attack in the U.S. in 2011. This was Yonathan Melaku who was arrested shooting at military recruitment centers in Northern Virginia. The NCTC does not classify any Islamic terrorism related attacks in 2011 however they list an attack by the ALF and the Arson Unit both animal rights groups.
In case no one has noticed that for the last several years the largest group of active terrorists in the U.S. are the "issue" or "cause groups". While the ELF was broken by the FBI the ALF and its offshoots continue to attack what they deem as targets of opportunity their favorite method of attack is arson.