Basic care-wise, I'd say as easy as corns, yeah. Comparing to corn snake care... Cooler temps (think lower 80s as your absolute highest temps--but I'll leave specifics to more experienced members), somewhat higher humidity, and a HUGE enclosure, and you'll have a happy rat snake on your hands.
They can get to be around 9 feet long, and are actually rather strong (as compared to, say, a corn snake of the same size). They are, indeed, semi-arboreal, and VERY active. The bigger the enclosure you can give them, the better--they WILL use every inch of space (floor and height alike) you give them.
How docile they are depends on the snake. Like any species, there are specimens who are particularly calm, and specimens who would just like to eat your face off. They tend to have amazing feeding responses, and, IME, aren't likely to differentiate between food and hand when they're in the "mood." They are also rather smart, curious snakes, and will often hang out in the open just so they can observe their surroundings (or so it appears--but I can't really claim to know what goes on inside a snake's head, can I?).
How long do they get, are they as easy as corns...etc etc. 
