chas, yes it's a tricky thing, and many of the comments don't really tell the performer anything ...
Some people don't post much, or anything at all, and I am not surprised if they don't comment ... but I have to say, that especially over the past couple of weeks there have been some really nice performances posted, with many comments ... It just amazes me that some of the 'regular' performers - who by their responses to comments appreciate what is said (even if it is constructive criticism) can't seem to take the time to let others know they appreciate - or don't appreciate - their efforts ...