Having actually studied the effect of various chemical, biological, and radiological threats as a member of a federal WMD response team, I would offer a few comments.
First off, I am in favor of a program that encourages people to prepare for contingencies like bad weather, power failure, etc. Preparations for self-sufficiency in such situations will have a positive effect WHEN there are further terrorist events. It is naive to believe that there will be no further attacks.
Chemical agents are not a meaningful threat to us in our homes. All nerve agents other than VX are liquids that simply evaporate and are gone. Their effect would be enchanced in a confined space, like a subway or a building. It is unlikely that a terrorist could deploy sufficient agent in the air over a city to pose a significant threat to the population. VX is the only persistent agent and would be a longer lasting problem if released.
Biological agents are worrisome, but those that are communicable, like smallpox, will turn around and bite hardest in underdeveloped third world paradises like where the terrorists come from.
Israel has not been bothered by WMD attacks. Simple explosives have worked well.
Draw your own conclusions.
Regarding the proposed use of plastic sheeting and duct tape to create a safe room, I invite you to review the following article:
Seems to be a current topic of interest. A report from Oak Ridge
National Labs.
"Will Duct Tape and Plastic Really Work?"
Issues Related To Expedient Shelter-In-Place
John H. Sorensen, Barbara M. Vogt
August 2001
http://emc.ornl.gov/EMC/PDF/TM_2001_154_duct_plastic.pdf Best regards!