I have written about dirty bombs at least twice before, and now here comes Steven Den Beste with that and more. It's terrific, check it out.
Some years back I had a Smithsonian magazine with an interesting article by Jeff Wheelwright, which had some interesting info on plutonium (Pu). I have looked in vain for links to this, but if you want to round up the article to see if I did it justice, have a ball.
Anyway, a large part of the concern about the health hazards of Pu was stirred up by the govt itself. Not because it was so dangerous, but because it was so expensive. Authorities didn't want anyone to steal it, so they played it up as incredibly dangerous.
But accidents will happen, and some men ingested Pu during the Manhattan Project. Several of them were still living into the 1990's, and still had detectable amounts of Pu in their urine half a century after their accidents. Collectively they're a very small sample, but in fact the group has lived well past life expectancies. I don't know if any of them are still around nowadays, and I spent some time looking on the web.
No, you don't want to put Pu on your wheaties, but as SDB noted, the stuff is way overrated. And when toxicity tests were performed on rats, testing was significantly complicated by the fact that Pu is extremely dense - it was hard to get it airborne so that the rats could inhale it, and rat's noses aren't all that high above the ground.
Here's what the feds say about Pu toxicity.
UPDATE: for a less sanguine view, see this.