There are plenty of offensive tools in the arsenal for cyber counterwarfare. Plenty.
I have to laugh at these jihadis who believe - quite wrongly - that the Internet affords them any anonymity whatsoever. It doesn't. Look at Aaron Weisburd at Internet Haganah, who with only a rudimentary arsenal has helped to put hundreds of jihadi web sites out of business.
Likewise, this EOM and his silly proxy is by no stretch immune from tracking. Any entity seriously interested in his identity and location could discover that info in a single evening session by watching his posts and source IPs. I assure you the USG has the capability to obtain ISP logs in a timely manner (hmmm, EOM thinks his ISP logs are "safe", haha). Which means EOM can be (and probably has been) busted. He's either an acceptable threat or none whatsoever.
I like to remind folks that the Dan Pearl murderers sent email ransom notes to several newspapers, and that they were then apprehended in less than a week in Karachi. Guess they didn't realize that those emails included the IP address of the Internet cafe they were using, and that the very long reach of the USG could go right to their front door.
These sick little jihadis with their monumental egos and incomplete logical faculties are seriously mistaken to believe they can outwit us. It's true we didn't pay attention pre-9/11, and it's also true that Clinton/Reno seriously hobbled cyber-intelligence efforts. But its a different world now, and the jihadis are under the microscope in a world where they are pathetic amateurs (shhh, don't tell them that). The Internet is the world's best tool for compromising their communications, because they believe it's safe, and they think they're real smart.
What a ridiculous joke they are, bringing another yet heaping pile of "humiliation" to the Muslims.
It's certainly possible to obfuscate your tracks pretty well on the Internet. It is not, however, trivial. It's especially not trivial if you're trying to hide from the US & Govt ... there are a lot of tracking tools available, the ISP logs just scratch the surface. It does take a certain amount of time and effort however - which is why it isn't done for every little jihadi posting. It's also a lot easier to hide from J. Random User than it is to hide from John Law.
But fortunately for the good guys, many of these people don't really have a clue how to cover their tracks very well. A few do, and they're probably the most dangerous ones.