Is there a situation in the English language where the "less" vs "fewer" distinction matters?

@mikeburns technically fewer is used only for things you can count and less is used only for things you can't count, but honestly, and this is coming from a former grammar stickler: language is a living thing, people will know what you mean if you use either in conversation, and it will only really matter to someone who prizes grammar conventions over communication and fellowship.

@checkervest
I was staring at a PSA on the train this morning that mentioned "one less worry" and my first thought was "probably should be 'fewer'" but then I wondered: when will we stop caring? Are we already there? It's a grammar rule that doesn't seem to resolve any problems.