People can be so petty, can't they? This is why you should only give as much notice as is considered culturally appropriate in the organization, and once you do, keep up with all of your job responsibilities until the very last hour. Other than that, all you can do is take the high road, and behave professionally yourself even if you aren't receiving the same treatment back.
If you must leave your job after three months - and I recommend staying a year unless you're totally miserable - then downplay the short tenure both in your resume and in interviews.
One of the toughest situations to be in is when you are objectively good at something, but realize that it's making you unhappy and unbalanced.
You never know when a new job isn't going to pan out, or circumstances change, and you'll want to return to your previous company. I myself have done this. While being a hothead about leaving a job may seem satisfying at the time, it's just not very likely to serve you well in the long-run.
If the job is not what you expected and not even your cup of tea, stay put and learn as much as you can while you carefully consider your next move.
Maintaining strong references is a critical part of effective networking, and I suggest sending your best contacts periodic updates, e-mails just saying hello, and holiday cards. Ideally, you should be keeping in touch with them at least a few times a year, so that when you need to give them the heads up that you'll be using them as a reference, it won't come completely out of the blue.
Try to keep your mouth shut until you have a job offer, especially if your move is not entirely certain. There are only a few cases in which I think it would be appropriate to tell your boss what's going on. For example, if your spouse is being forced to relocate, obviously you are going to go, and if you have a good relationship with your boss, then it might take some stress off of you to tell the truth. The general rule, though, is not to give your employer more power over your destiny than you have yourself.
