abc3:
You are right. It is human nature to continue to worry. Some people are better off and are happy-go-lucky type and you are one. And I wish I could be that way too but can not on immigration matters.
Purely from legal standpoint, after GC approval you should go work for sponsoring employer, if not already. However if you invoked (not quite "filed") AC21 and communicated to CIS, you are fine and covered under the law that you ported to a same or similar occupation job. However, if at the time of Naturalization (chances are extremely rare, but do exist), CIS can check if you worked for your GC spoonsoring employer after all or not and if not, may be grounds for invocation of permanent resident status.
I am in similar situation. My GC was approved a few weeks ago and after consulting with a team of lawyers from my side and my wife's, I have submitted my resignation to an excellent full time, extremly well paid position with a Fortune 10 company.
Its your decision at the end and your risk taking capabilities.
Sun