I too am a Ginny! And I also have been called Guinea! In fact my online name which is also a nickname my mom has called me for years) is derived from this.
Once I asked the ignoramous if he had ever heard of anyone named Guinea. He just didn't get it.
Mostly I get called Jenny. My old boss would get really irritated by this and correct people (he would actually spell it for them).
Spelling - wise, I have seen Gennie, Jinny, Ginnie, Gina...you name it!
My last name is relatively simple - but gets mauled almost as often.