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Modern exterior lens coatings are really tough. You'd really have to try and damage them...either a drop right on the element or cleaning it with sandpaper or something. Interior coatings can be pretty soft though, and very easy to damage. Spit on it, wipe it with your t-shirt, and the bubble is gone.
Oh, and Doug--try a Dremmel tool with a felt polishing pad and a really mild abrasive (I've used cold cream believe it or not). That was with really old coatings though...you might need something more aggressive with the new stuff .