Regarding Polonium 210
Radioactive isotopes are much in the news lately because of last week's death of former Russian spy Alexander Litvinenko. The specific isotope found in Litvinenko's body is a really nasty one if you're trying to kill someone -- Polonium 210. In the non-spy world, polonium is best known for it's very high power density, although its relatively short half-life makes it not very suitable for things like longer space missions. For the nuke geeks out there, 210Po84 is made by a β- decay chain from Pb-210 to Bi-210 to Po-210; the Polonium alpha decays to Pb-206 with a half-life of a little over 138 days, with a decay energy of about 5.4 MeV. This relatively moderate half-life, which means it lasts long enough to deliver it to the target but still decays rapidly enough to cause serious damage, makes it one of the "worst" alpha emitters.
Still, unless it's ingested, it's not going to cause random bystanders any problems -- despite the warnings of articles like this one that persist in calling it "plutonium". Much like "depleted uranium", this is one of those things that probably serves to scare the public about anything having to do with radiation more than anything else. Remember -- if it's an alpha emitter, it can't hurt you unless it gets inside your body, and if it has a long half-life, it most likely won't even hurt you then.
(Disclaimer: I should point out that as a former Navy nuke, I have a kind of institutional disdain for alpha-emitters; it's the neutron-emitters that scare the crap out of me. Contributing to this is the "Great Neutron Conspiracy" that exists in the Navy Nuclear Program. For those who don't believe in the GNC, I would ask you: why is it that dosimeters that monitor for neutrons are sent off the boat to be read? And why are the neutron-"detecting" radiacs the only ones we have to send away for calibration? Kinda makes you go "hmmm", doesn't it?)