I love the Exposures catalogue <img src="/images/graemlins/smile.gif" alt="" /> It does have lovely stuff in it.
My understanding is that any sort of sticky substance on the back of a photo is naturally going to harm it, because it's a glue that's holding onto the photo. So if you ever want to remove it, something is going to rip. And anything that presses down on the front of the photo is going to damage it for the same reason. So you're safest with photos that are held down to the paper by the corners, and that just have another piece of paper lightly resting on top of it (i.e. the back of the next page). That way no moisture is trapped in there, no glue or plastic is pulling the photo apart.
I guess even with all of that I don't trust photos to last eternally, and am making sure I have all the good ones scanned, because I can always back up JPG files infinitely long <img src="/images/graemlins/smile.gif" alt="" />