I really like Nik's Silver Efex in that it allows you to very quickly make great B+W conversions in lots of different ways. I notice a lot of other people use it on this site. One problem I find though is that it is terribly prone to 'image halos' - white lines around images within the frame. These sort of halos are generally associated with 'oversharpening' which would mean pushing the 'sturcture' sliders too far to the right in silver efex. I certainly try not to do this but I still get these 'image halos' - I wonder if anyone knows what I am doing wrong. As an example I post below a pic I posted in the PP7 challenge - you can see the halos on the 'overhead wires', the 'top of the building on the left' and the 'legs of the person on the right'.