My results differ. In fact, I just left a tarnished rosie in 100% acetone for 10 minutes, just like I would do with lemon. The tarnish only diminished on the high spots that I rubbed the crap out of afterwards. Not sure by what mechanism acetone is supposed to cut through tarnish, anyway. It is a solvent. Which means it may cut through grime... but tarnish is not just stuck-on grime. It is a layer of corrosion on the surface of the silver. I've tried acetone unsuccessfully multiple times in the past and here again. I stand by the idea that lemon juice is better at breaking down tarnish than acetone.
If your coin is nicer than a rosie, though, it's probably best to NOT use lemon juice on it, though. If the tarnish is too deep, you may see pitting that was hidden by the tarnish. Acetone will loosen stuck-on dirt, just like soap and water... but still, don't finger-rub it after or you WILL polish it. Rinse only.