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I worked out the brightness of a typical 532nm 5mw laser pointer at various distances, to satisfy my curiosity that they were not dangerous to planes past a certain distance due to beam dispersion.
It turns out, when I use my own 5mw Ebay special, that the beam dispersion is in the order of 1 metre per kilometre.
The illumination of the beam is about the same order of brightness as a car headlight at 1km. Because it's effectively a point source there are visible diffraction effects and the brightness will vary a lot very quickly (the exact same way a star would) making it something that attracts the attention.
Aircraft at cruise directly overhead are ~10 km distant, so the beam is ~10 metres in diameter and definitely not an issue for direct vision.
It gets less and less bright the farther away from the zenith the plane is. At 80km the pilot would have a pretty hard time seeing the laser and certainly would not be affected by the illumination.
Now, illumination of a hovering helicopter or a plane on approach is a completely different matter and certainly can cause a startle effect. But no physical damage would be possible from a <20mw laser out past a few hundred metres.
I don't like that pilots have to deal with the startling effects of a sudden laser illumination, but I dislike the overhyped response of the aviation community and authorities to the pointing of lasers at aircraft.
Regarding the use of lasers for pointing, if you can keep them above e.g. 10 C, they are great for being able to locate with one scope and use others to observe. I used an 80mm scope on a goto mount, with a hacked-together laser finder to sky-point while using another scope to observe the object in question. If you are any bit handy, a dewstrap along the pointer with insulation around the whole lot will keep the laser diode and batteries warm enough. I used little rechargable pocket warmers with the sodium acetate filling - worked a treat.
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