The Japanese cult tried on two occassions to disperse bio and failed miserably. There is an excellent article at world net daily. You can find it at this url: http://www.worldnetdaily.com/news/article.asp?ARTICLE_ID=24785
Chem/bio can be effective, if done properly. But that's a big "if". I've been pleasantly surprised at the number of articles and media reports that have begun to downplay chem/bio as a threat. Most of the earlier reports were almost hysterical in tone. If you listened to those reports, you could only wonder why any one would ever build anything other than chem/bio weapons. Finally, some folks began to ask the question: "if these things are so good, why haven't they been used?" One obvious answer is that it's much more difficult to do than most folks think. I even saw (FoxNews) a reporter back a chem/bio "expert" into a corner, finally getting him to admit that he and many others were grossly exagerating the chem/bio threat. He said that was the only way to get attention. Of course, that only raises the question: "if this stuff is so much of a threat, then why does one have to exagerate in order to get attention."
That said, chem/bio can be deadly, but there are usually better ways to achieve the same results. (I've seen news reports that indicate it would take a ton of chem to attack two square miles. That's pretty efficient but where does one get a ton of Sarin? I'm sure it's a special order even at Walmart.) I wouldn't expect a lot of casualties from the kind of attack these terrorists could manage, but the psychological impact could far outweigh any casusalties caused.
Luckily, it IS apparently quite difficult to do, so hopefully none of these nuts tries it out.
They could have stompped their feet, held their breath, or thrown their poopied diapers around, all of those would have got some attention.