Sure, it makes us nervous, but no cities have been targeted, and it's not a widespread event that is showing up all over the country. I haven't picked up the mail yet this afternoon, but I'm not too concerned about it being deadly.
At worst, it sounds like a terrorist got ahold of some anthrax, and it appears that a plan to spread it through crop dusters was in the initial planning stages. It looks like the jig is up on that plan, so our resourceful little terrorist is mailing the spores to the media. It's not a very effective way of spreading it, and as a terrorist attack, it's pretty much a dud so far.
If this is the worst the terrorists can do to us, we're almost home free.