There's not really any cases....yet. Only time will tell, once more of the cars have higher mileage on them. I have a feeling that Mitsubishi may have nitrided the cranks though, after realizing the clusterfuck with the 2G Eclipse/Talon Turbos.

Keep in mind, that technically, any motor can crankwalk at anytime though. No line of cars are "invincible" from a walking crankshaft, the 2Gs just seem to have a more widespread problem, do to Mitsubishi screwing up straight from the factory. It's been a debated topic for years now and there are many different theories, but no one knows for sure yet. Even the mighty 2JZ-GTE Supra motor has had reported cases of crank walk before.

Best thing to do is just take good care of the car. Continue to learn/research your car as you own it over the years. I think doing small things (like using good ful synthetic oil), helps to prolong your motor life and somewhat deter crankwalk. Doesn't mean it'll make the car crankwalk proof, but it can help. If the motor has any issues that can cause the crank to walk (out of spec manufacturing, non nitrided parts, etc) it'll eventually walk, no matter what you do.

Good luck with your find. Both the STi and Evo are excellent cars. I personally prefer the inline 4 design, but the boxster motor is very potent and robust as well.