One of my biggest pet peeves is people who have no respect for the email subject line.
As for search: that takes skill too. A lot of the same people who don’t bother to learn file systems just skim the first page of Google or Spotlight results and call that search.
I don’t think there’s a single right answer. I use search a lot – but when it fails (or takes forever because of what I’m searching for, what I do/don’t remember about the specifics, the commonplace nature of the relevant terms, etc.), it sure helps to know how to dig through the file system. Vice versa as well, of course. And to have a relatively consistent file naming system.
This feels a bit like debating whether screwdrivers are necessary now that we have power drills. Feel free to limit yourself to a subset of the available tools if that works for you! I’d rather have them all at my disposal.