Today (Sept. 11, 2011) marks the 10-year anniversary of the 9/11 terror attacks in New York, Washington, D.C., and Shanksville, Pa., that took the lives of thousands of innocent victims from America and the world over. But to many, the memories of those events seem like just yesterday. The anniversary obviously marks a time for reflection, and while Twitter wasn't around back in 2001, it now is a very popular destination for people -- ordinary citizens and the famous alike -- to offer their memories, thoughts and prayers. Rock stars have feelings too, of course, and here is a sampling of what some of them are Twittering about on 9/11. Check back often as we may add to this list as the day goes on: