well as ever the main problem is the amount of photographer and the pressure on the bird it results rather than these practices which to me may not be harmful if use sporadicaly by a single photographer during the all breeding process time. The problem to me is that photographers tends to go always to the same places and are attempting to get picture of the same birds, after... It is particulary true in Hongkong with probably some of the highest density of photographer in Asia, but also true in most of famous reserve in Asia...then I would totally join Geoff in his concern that even a different single photographer (it is often more than that) attempting everyday to take a picture of the same bird using playback create a big disturbance to the bird and reduce greatly its breeding success...In the other hand, a photographer that would go to any poorly visited place finding its own birds on a remote trail and use playback to get pics of it would be to me a minor disturbance...But I'm not sure that it is even possible in Hongkong...
To me the pleasure to get a good picture is not only to press the shutter, but all this process before that lead to the finding of a great bird and the solution found to get the right pic which often do not require any playback, but just a good analysis of the bird movment and favorite perch...
Feeding bird come to the same category to me.
Picture at nest would require hight binding precaution that I'm sure nobody are taking and are definitly best banish as a conservative approch...there is dozen of solution to take picture of birds without creating any disturbance...the best of all to me are a bathing pool, since birds are always very alert and cautious (so isk to put the bird in danger is reduce) when go bathing and it can provide great proximity...and most of bird species are drinking and bathing almost everyay...then just need the right weather and place...