It didn't kill the magic for me permanently, but I will say that around Christmastime, being away from my family and working those LONG hours really upset me, and made me hate the mouse a bit.
Disney is a big, big company and Disney World is a big, big place. Management and rules are definitely not consistant within the parks or even the areas. I think if I worked under certain people, it would have killed the magic for me.
I did love it, and although I wish I was in a different area and had a different role, I would do it in a heartbeat all over again. Sure, there were days that I did NOT want to go to work, days where I longed to be a guest again. But the good far outweighed the bad.
Now that I'm gone, I miss it SO much, I have my March trip and my May trip booked already!
I had no problem going back after being a CP and still felt the magic. I'm not sure that it's the same way for everyone though.