What's the reason? It's all in the reason. Family health crisis? The employers lied to you? The ED is dangerously understaffed? The doctors lounge doesn't have your favorite pop tarts and 5-hour-energy drinks?
The reason is everything.
Absolutely. I also think there is a generational aspect. For people my age and older, it was drilled into you in medical school and residency that the absolute worst thing a physician could do or be was to be a quitter, not a team player, or appear lazy. As explained to me during a ward rotation, actively killing a patient at the bed-side would always be viewed as better than even resurrecting a patient from home or the call room. Unless you were in the ICU or morgue, or a member of your immediate family was being buried that morning, you showed up for work. In the same way, the concept of a physician not fulfilling his contract was inconceivable. For people from this generation, the idea of leaving after a couple of months will always induce a negative Pavlovian-type response. (The positive aspect was this type of loyalty was generally considered a two-way street.)
Now, that has changed. One can debate if the change has been for the better or not.
With that said, it depends on the circumstances. If it is due to an illness or similar issue in the immediate family, it should not be a problem. If there is a serious ethical/legal issue, just go ahead and leave. If it is a matter of personal comfort or money, the type of practice you are leaving will play a role. If it is a 60-person group where physicians are coming and going all the time, there will probably not be any repercussions. On the other hand, if you are bailing on a 3 person group and leaving them for an extended time as a 2 person group, they will probably be upset and potential hiring physicians "of a certain age" will not take kindly to it.
It also depends on how your current group treated you. If they took a gamble on you (lesser record than they normally hire), or paid for you to move, or gave an above-average salary, then leaving for comfort will be viewed very poorly. On the other hand, if they gave you nothing exceptional when they hired you - you were a typical hire and got the standard deal - your expected loyalty to them is also lessened.
To summarize, leaving after a couple of months is never good. It might be the only responsible action, it might be the lesser of all possible evils, or it might be considered selfish. Then again, if hospitals and groups are doing what is best for them, the old attitude of physician loyalty (see above) really doesn't apply either.