"nor do I want to spend the effort tagging all my stuff so that I can use search to find it. That's why my filesystem is hierarchical."
Technically you are already tagging your files by using filesystem hierarchy.
Nepomuk could do tagging easy and automatic (for tags that can be automatically generated, existing directories as tags, ...), but unfortunately it really doesn't. It is getting kind of silly that finding content on web is easier than on your own desktop machine.
I type a string in google and I usually get what I want - in kde with nepomuk and strigi enabled, "alt-f2" search almost works, but only if the search result is unique. With dozens of results, no preview or context is shown, only the name of file - Useless.
Chromium history shows me what I surfed yesterday with a single click. But with all the nepomuk indexing, I can't get a history of what local files I read and edited yesterday.