I believe optical touch to be sort of like what Microsoft did with its PixelSense (formerly Surface, before they announced their Windows 8 tablet).
I tested that thing briefly at school (with only the Bing app, lolol, so useful). It works fairly differently from other touchscreens.
You don't actually need to touch the screen. Just move close to it so the screen "sees" you. So you can do "telekinesis", bringing your hand close to the screen. This can be fun (and almost scary xD) and even practical, but I guess, also cause errors.
Since it literally sees things coming and going, their shape and all, it can be considered smarter. It sees your finger; it's able to know it's your finger. From shape and/or thermal reading (because I think it works with infrared). It sees another finger; it acknowledges it as a different object, and remembers it when it moves. Your finger is back? It remembers it. Paintbrushes, etc. should work just the same.
It knows the shape and remembers it. This makes it so that things can't teleport around the screen in a buggy way like capacitive screens can do. It doesn't acknowledges touches, simply, like your common touchscreen does. It acknowledges what it is, and how the software cursor for it should move/be changed knowing that this is this object. Leads to less confusion, in theory, when moving around many fingers, for example.
Capacitive touchscreens see a point, where you touch with your finger. Optical ones will see a round with the shape of your finger, including your nail. So if you put cookie cutters on such a screen, well, open up any visual art app and you can draw shapes from those cookie cutters.
And also, since it can identify objects, uhm, let me give you an example. You're in, say, Photoshop, and you're painting things with a real paintbrush. Well, in theory, assuming the software is all programmed for it, you can tell the screen that your arms, hands, body and even chin can lie all over the screen, but will do nothing; only your paintbrush will, as well as an open hand to move the document around, and a single pointed finger to select menu items. So you could paint naturally, your arm resting on the work area normally, and your arm shouldn't mess with the controls.
It works with more or less anything. For example, in some application, you could paint with an actual paintbrush, and the screen would more or less see each bristle and produce a realistic stroke. I saw something like that in a PixelSense ad, I think. And since, unlike capacitive screens, it doesn't rely on power conductivity (presence of water/iron/whatever), well, literally ANY object can be used to manipulate it, as long as it's not invisible to an infrared camera. So using gloves or any damned item as a stylus with this screen shouldn't be a problem.
Oh yeah, and since the PixelSense works with infrared, well, it's quite warm to the touch. Adds to the "whoa, telekinesis!!" buzzing experience. x3 But this probably makes it sort of unsuitable for tablets and smartphones, for example.