I've had several crankshafts crack at the drive side mainshaft, right at the angle between mainshaft and counterweight cheek, but didn't take any pictures, just chucked them. Fortunately, there's a characteristic onset of vibration when they crack, and it's pretty recognizable. It starts as a vibration at redline, and then spreads to progressively lower rpm, and finally breaks. The vibration also increases in magnitude as it spreads down the rpm range. The last one I had do that took two laps at Willow Springs to go from a vibration that began at 7,000 rpm to one starting at 5,500 rpm, and that's when I shut it down. It was a factory short stroke crank, with the usual radius the race shop machined at the junction of mainshaft and cheek, as well as being shot peened, but it still cracked, and would have grenaded if I'd kept going. To be fair, it did have a lot of race miles on it. Most of the cracked crankshafts I had were discovered during teardowns. I always checked the crank and rods for cracks when I had the engines apart, but that was back before billet cranks and Carrillo rods. I did have one that cracked at the drive side rod journal, but we discovered that the cavity in the journal was off center a lot, and that the metal was thin at the location of the crack. And yes, the journal had the proper radius. I'm pretty sure that the mainshaft cracks are a result of fatigue from the mainshaft bending at the cheek as the crank speeds up and slows down with each power pulse. They always seemed to start in the same location on the shaft circumference. Just my humble opinion, though.
Like Rohan said, grinding the journals undersize without the radius is a guarantee of eventual failure, at least in a race engine. I never experienced that problem, but I've known a couple racers who have. Most automotive crankshaft grinders are reluctant to dress the large radius onto their expensive grinding wheels, because they just have to dress the wheel down to a smaller diameter afterwards to get a sharper radius for their automotive work. Those large grinding wheels aren't cheap, and the shops are reluctant to use them up any faster than they have to. Fortunately, there are at least a few shops around the country now that are willing and able to do the Norton cranks properly.
Ken