I have these little things in my planted tanks. I did read that they are a type of little snail or maybe copipod/amphipod, although, like you said, they are little more than a dot. Mine move along the glass too, very slowly. I don't really watch them move but I'll look at the tank and then look again in 15 or so minutes and see that they have moved along the glass.
I have had these things in my tank for over a year now. I think I got them with the plants. I looked at the tank my plants came from and saw the little snails too. They are not harmful at all. Sometimes I'll see more of them on the glass and sometimes I'll see them on the plant leaves. Once in a while my fish looks very intently at the gravel and then "snaps" like he's eating one of these things. They may eat algae, although it wouldn't make a difference in your tank like some algae-eating fish. One time I saw little trails on the glass (the front glass was kind of green from algae) where they moved along and ate the algae.
I wouldn't worry about them or put a big effort into removing them. The population seems to come and go. Sometimes I see a lot and sometimes I don't. IMO they are only annoying when you want to take a picture! Before taking a pic I'll get a paper towel and swoop over the inside of the glass to remove them or at least knock them to the substrate. Other than looking bad in a picture, they are not a problem.
