The interview is straight forward, not many surprises, the gouges are all over, and are extremely accurate, so look them up, print them out, and study what they say. For the written portion, I studied the ATP gleim, and the yellow, "Everything explained for the professional pilot" book. I was the first one finished and I got in there late. The sim is silly really, if you don't know your instrument stuff, he will know, but if you do, it's a walk in the park. So if you haven't been under the hood lately, get on FlightSim and shoot some approaches, and how to enter a hold. The HR portion is actually kinda fun, you get to know the guys, and talk about yourself, Bob Trout is great to talk to, they just want to see if your normal. They will offer you the job right there.
I would rate the training as semi-difficult, no one washed out of ground in our class of 10, but we did loose 3 or so during Sim. The sim does push everyone to their limit of what they can do. And you need to be able to go in there every day, for 4 hours at a time and at odd hours, and perform.
As for working for them... I like it so far!!! Good luck!