Fact: Nikola Tesla did not use a respirator, and he is currently DEAD!
Sharing my own stupidity here for all of your sake:
I was angle grinding some sheet metal the other day, and when I got done, I blew my nose (I have allergies right now). The snot that came out was a nasty greyish goo.
I had been inhaling metal powder, which I can't imagine is good for me.
Respirators are super, super cheap, and you should wear one. I left a pack of them on top of the tool box by the safety glasses. If you're sanding wood, or cutting metal, or welding, or doing anything that makes nasty fumes, put one on. I have another box laying around the house, and I'll bring those in too.
(These are left overs from Burning Man -- ended up buying a shitload to give away, and then didn't end up needing to give them away)
-Ryan