I seem to be in a bit of a minority on this one. I make it so that certain items (jars, crates, cupboards, that sort of thing) will often have an item, but by no means always. I think, as Hain says, that good exploration should be rewarded. I do not use sparkles, exclamation points, changes to the mouse cursor or any other of the myriad ways that exist to highlight items, because I think it ruins the whole point of having to look for things. If something is important, or I think that the player may need that extra healing item, then it goes into a chest, and so becomes obvious in that way.
As for putting comments, I occasionally put one on something that doesn't have an item, but I keep it rare, because unless you are something of a writing genius, by the time you are up to your 500th blank item (and think about it, that's not an exaggeration by the time you include all the things you could interact with. It will end up higher than that) you will have repeated yourself so often that it is both tedious to write and tedious to read. I put comments on found items sometimes, but not always, or else use it as a way of having some interaction among members of the party.
So long story short: I don't mind having blank interactions.