There's not a limit - the issue is more a matter of how the photo/art is represented by the photographer (this is my issue with Peter Lik). As long as you're honest about the process, it really doesn't matter how much you photographed something. It's up to the viewers to decide whether they value the work more or less depending on whether you Photoshopped it or went to great lengths to get the same result in-camera.
Awesome bit of Photoshopping, by the way. That long exposure look works great for Sydney Harbour!
Lol, Peter Liks moons. I don't feel the need to disclose that something is Photoshopped but I don't lie to people either if they ask. Nor do I claim that everything is "in camera"
Exactly!!!