While it's not very pleasant to inhale large quantity of any dust, some are much worse than others. Here we try to collect some information about different dust types and their possible effects.
Keep in mind that this page is not a complete overview and everyone is responsible for their own materials, so do some research whenever you are not sure!
Regardless of how dangerous "your" dust is, the best option is not letting it reach your body in the first place. Also keep in mind that many dusts are very mobile and may harm the people around you!
- extraction with a shop vac or dedicated dust collection system at the tool
- filtering a tool's exhaust and collecting the dust
- extraction around the workpiece with a sanding box or vacuum table
- wearing a suitable dust mask or respirator
- wearing long clothes to avoid skin contact
- filtering fine dust from the entire room's air (we're working on that for our woodshop)
- NOT blowing a workpiece "clean" with pressurized air
(Heavy) Metal Dust
Examples for toxic metals you may come in contact with are lead (e.g. when sanding or blasting certain paints) and chromium (e.g. when grinding stainless steel).
Wood dusts are different for every species and can cause breathing problems, allergic skin reactions and some perhaps even cancer:
- Hardwood dusts like oak or beech are known to cause cancer, softwood dusts should be treated with care as they may also cause cancer. 
- BGHM: Arbeitsschutz Kompakt Nr. 077 - Gefährdungen durch Stäube
- BGHM: Holzstaub Gesundheitsschutz (also contains valuable information for planning a dust extraction system, e.g. minimum air speeds and where to measure)