Is it OK for traces to come off SMD pads at the corners?
I do it all the time. I like the way it forms nice smooth 135 degree angles trace to pad, pretty much no chance of having etchant traps. On the other hand, you need to be careful. Depending on the component size, having traces come off pads asymmetrically can prevent them from centering during reflow. I've never had a problem with this with anything 0603 or larger. 0402 and smaller, you better think really hard before doing it. It helps to keep your solder mask as tight as board house tolerances will allow.