I have no first-person experience with this thread, but a co-worker of mine is doing this right now. We work on an NICU, and we had, to put it bluntly, a terrifically sucky manager who was way too busy to take any time for us. Well, my co-worker decided she was goign to switch to days and move to one of the other units within the hospital who'd listed a job opening on the job board. She went down there, interviewed, hit it off with the other unit manager, and they offered her the job on the spot. So, she goes to put in her resignation notice and filled out the formal transfer application to move to the other unit.
Now, before I go on, let me say this. This nurse is EXCELLENT. She's conscientious and compassionate and extremely bright. She's been a passionate advocate for a number of relevant issues on our unit, and has been generally a huge asset to the team. In the last six months, her three children all came down with the chickenpox, and she'd missed some work because of it, but had done it within the rules of our facility and had provided documentation, etc. Otherwise, she's never missed a day of work.
So, the new manager contacted our old manager to verify employment and apparantly asked something along the lines of "What is your opinion of this employee?". Our manager said, knowing all of these things about this nurse, "Well...I...I don't know her that well, really, so I couldn't say. You're welcome to come up here and look at her record, but I can tell you that she's missed quite a bit of work recently."
So, the new manager called her in and said, Well, your boss didn't really seem to speak very favorably of you. Is ther anything you need to tell me about your chronic absenteeism? CHRONIC ABSENTEEISM?? Come ON.
Furthermore, in our facility (I just left there, actually), your current manager can hold you for NINETY days, not thirty. So she decided to hold her for ninety days, the other job was filled by someone who could start sooner, and now she's stuck here unless she either quits or tries again with a new opening on a totally different unit.
So, IMO, that's your worst-case scenario.
I freely admit that my old facility is terrible, so I wish you the best of luck!