As many other posters have said, I don't think its being in nursing in general that has made a change in me, so much as life itself has changed me. Nursing is a much harder job than you are prepared for in nursing school - at least that was my perception at 23 when I was newly graduated.
You do begin to be able to sniff out the BS'ers - the frequent flyers, the drug seekers, the obnoxious demanding pts/familes, the antagonizing managers/supervisors - at 50 paces. You see things that you can't hardly believe are happening to people in your part of the world - meth heads whose children live UNDER the trailer - not in it, parents with no idea of good parenting skills and no intent on finding them, people in obviously toxic relationships - things you hoped happened somewhere 'out there' in the world.
You realize that management doesn't give a flying flap about your personal well being, they just want a warm body on the floor and don't much care that you think your assignment is dangerous. That nice story about nursing being a calling that you learned in nursing school? Well, that may or may not be true, but your employer really doesn't care about your empathy for the patients as long as the Press-Gainey scores are up. You can be the most caring nurse in the world and all it takes is a couple of post cards from PG saying you didn't get their ice water quick enough and you get called on the carpet.
That being said, I remain very compassionate for those people who are truly ill or in need. Even those whom I think are just milking the system, I remained very pleasant and calm towards them. It was my job to take care of them, and part of that job was to keep my thoughts to myself. And that extended to keeping my thoughts about certain annoying as H---fire co-workers as well!!!! Keeping my mouth shut has saved me a lot of trouble, once I learned to do that!!!!
Its just that life and the things you see and experience change you, and some people are just the way they are, regardless. I no longer work at the bedside, and for me, that was the best thing I could do for myself after 24 years of nursing. I've been at my present job for 5 years and I really have become much less 'hard' on the outside. I am again a nice warm ooey gooey person that I've always been underneath.