This is a thorny issue, and it’s too easy to cause unintended offence by email in general, and in this situation by casual logs. I personally feel uncomfortable telling somone their cache is a load of rubbish (although have been unable to contain myself on a couple of occasions, tut tut). In this situation a simple “TFTC” can be used as a cork in a bottle that is best kept shut. Having said that I think maybe people are busy and in too big a rush to log their finds to spend the time thinking of anything more, and no criticism is being implied. That’s the problem though, you don’t know what the finder really thinks of your cache. As regards long series, there’s no way I’ll be able to remember them apart, so I make paper notes as I go along, just to put something meaningful in the logs as I agree that cut-and-paste logs are a bit lazy.