Originally Posted by patthebrewer
Think of die grinders as broadswords, and dremel rotatary tools as a surgeons scalpel.
Seconded - great analogy. I have both a die grinder and a Dremel and they're different tools for completely different jobs. That said, I find myself using the Dremel far, far more frequently than the die grinder or just about any other tool in my shop. The bits that I use most:
Flex shaft attachment - using the above analogy, the flex shaft is the attachment that turns the Dremel into a scalpel. Before that it's more like a paring knife.
Tungsten carbide cutter - I tap threads rather than welding or using nuts when mounting things like pumps or casters. Often I need to enlarge the holes in the mounting plates to get all of the holes to line up. The tungsten carbide cutter is far and away the easiest way for me to do so.
Stainless steel brushes/cups - easiest way to clean tight areas like where my fittings are brazed on.
Cutoff wheels - this is the scalpel vs broadsword thing.