With a nick like yours I assume you've spent some time in Utah where all the good stuff has been bunkered. I seem to remember the Japanese cult used Sarin and not a biological agent. Was there another attack that I missed?
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.