I wear an old organic vapor respirator when dry sanding. I wear no mask when wetsanding, and a brand new organic vapor respirator that is stored in the freezer in a plastic bag when spraying.

The vapors in modern paints are really nasty, but the solids in them are plastic/oil based. They can't be too good for the lungs. Some fillers also have fiberglass, which is nasty stuff.

I wipe down vehicle surfaces and hose out the garage periodically to remove dust. once in awhile, I blow off my shelves (with a mask).

I have a fresh air system that is so annoying that I don't use it (even when spraying). Mainly dragging the extra hose that supplies the fresh air is annoying. It also gets hot, so I would run a piece of the hose wrapped in a coil through a bucket of water to keep the air cool. And lastly, it is loud - both on my face (with a hood) and outside where it is doing the sucking - sounds like a vacume cleaner.

I've decided for myself with the minimal ammount of painting that I do that organic vapor respirators are safe enough.