I was probably being somewhat disingenuous with my original post but I am glad it has generated some interest and overall agreement about the need for level horizons when they are meant to be level.
The fact is that last night I was looking at the Recent photos on the gallery and was amazed to see pictures with tilted horizons. It was still there this morning, but I then looked back at well known users here and sure enough there were more. It makes me wonder just how people can do this, when surely it is patently obvious that photographically, nay by the laws of nature, wrong
The thing is, it seems to me, the vast majority of images posted in the gallery are of birds, (shouldn't they be on the bird forum

) insects, flowers, wildlife and so on. Level horizons are usually not an issue with such shots and perhaps people forget when it becomes one. As has been said here already it is easy to correct in the software, not to mention making the photos look better.
I find sometimes it is difficult to know if a pic is definately level especially when using wide angle lenses, especially when there is little in the way of reference points within the image. In response to Adeys request for blue sky against the yellow field,
HERES a shot taken a couple of years ago. I think its level