One of the holy grails I've been working on over the past month since I got my K-5 is moving trains at night. It's tricky because you have to have a fast enough shutter speed to minimize the motion blur, a low enough ISO to minimize noise, and the right f-stop to maximize sharpness. After trial and error over the last month, I think I almost have it. (I think I can slow down the shutter speed further since this is a slow speed area.)
ISO 1600, F/2, S 1/100, 50mm F 1.4 K prime.