A couple of yeas ago, the outfit I fly for got rid of our Cessna 414 and got a King Air B200. They did send me to FlightSafety, and after the FlightSafety Initial Training Course (5 days), and a couple of flights with a King Air pilot with a lot of time, I was comfortable flying it single pilot PIC. My biggest challenge was learning the new autoplilot/FD and EFIS (intimidating at first, but after a couple of flights, it became intuitive - and easier to fly than the "old stuff") and the Universal FMS that was in the plane.
Bottom line: I think the King Airs are a little bit easier to "fly" than the 400 series Cessnas, but like the others said, a bit more complex (and different) systems; maybe some avionics to learn too. If you are only going to fly SIC, I wouldn't sweat it too much, it's a really nice and easy ship to fly, no bad handling characteristics at all that I can think of. But try to get ahold of a FlightSafety or Simuflite Training Manual from someone who has been through one of those courses before, and READ IT THOROUGHLY.