google了一下Eb1b, Perm拿到绿卡后180天内换工作对绿卡及今后入籍的影响，把感觉
较权威的说法整理了如下。。。
pjiang 说( http://blog.wenxuecity.com/myblog/14332/200807/22543.html )：
"""
其实，并没有任何的条文规定，拿到了绿卡之后不能马上更换雇主，更没有 180 天之
数见诸文本。这完全是为了自我保护，避免 fraud 的嫌疑及将来入籍时可能引起的麻
烦。
...
在入籍申请时，有谁因为拿到绿卡之后迅速离职而被拒？老师未曾听说。
"""
但同时又说：
"""
在拿到绿卡之后就迅速地离职，雇主告不告你并不重要，如果移民局因此而认为有
fraud，那才是麻烦。
"""
有点不明白，既然没有听说有谁因为拿到绿卡之后迅速离职而被拒，为什么又提到“移
民局因此而认为有 fraud”，怪吓人的！
下面的说法更吓人了（ http://immigrationvoice.org/forum/forum5-all-other-green-card-issues/3305-changing-company-after-getting-green-card.html ）
"""
Clearly, the law before AC21 was passed in October 2000 required that a
person continue working with the employer that sponsored the green card for
at least 6 months to 1 year after obtaining the green card.
...
The official rule (which IMHO has not changed with the passage of AC21) is
that you must not have any preconceived intention to leave the job when you
get your Green Card. (Your friend clearly does :-( ) In general, working for
the company for one year after getting the GC is normally considered
sufficient.
"""
高手或者过来人说一下Eb1b, Perm拿到绿卡后180天内换工作对绿卡及今后入籍的影响
吧。。。