The thing is that I can of course guess that if no visible action is taken, that the moderation team disagreed with the report: I might want to know in some instances, though why they disagreed. - Just as reasons are given when a post gets moderated. Of course I don't expect a thread to be opened up for every post that didn't get moderated and the reasons why: A PM would be nice, though.
Also, I just like to hear after a while that my report has been looked at at all. It might not make that much of a difference with what happens, but it gives me the knowledge and feeling that my report has at least been looked at.
I guess that others feel similar about it.
If that would mean that the one to two minutes per report add quickly up to hours of work for the moderation team, I'd understand why they just skip it. I can also understand that the moderation process takes some time, given that the moderators have a real life and are spread over different time zones.
So, that said, I'd like to see a policy for how to handle reports that aren't acted upon. I'm also okay with a policy that says "We don't give feedback if we don't see the need to act on a report, because we don't have the time to." or something like that, as long as I know what I can expect - though I'd be happier if I'd be able to expect to get some kind of feedback after a while.