I have one of the radioactive thorium-glass Super Takumar lenses. Aside from yellowing (cause by decay products of the thorium, and I'm told that a few weeks under UV light will correct it -- trying to find an economical way to set that up without exposing the lens to the heat of direct sun), it's an excellent lens indeed - but based on my experience in the last few months, not enough better than my Tessars and Skopars to be worth the risks of grinding the thorium glass or the expense of properly disposing of the radioative and toxic residue.

As noted above, there are now glasses that effectively duplicate the optical properties of these radioactive glasses without the potential health issues. However, I'm not getting rid of my Super Takumar -- I don't store it in the headboard of my bed, or use it as a loupe, and I don't consider it any more hazardous, when stored with my camera gear and used on the camera as a lens is intended to be used, than ordinary photo chemicals used in their common applications.

Would I buy another one if it were crystal clear, clean aperture, and otherwise good condition? In a heartbeat, if I could afford one (and I might, before too much longer).