Ok I have some questions. Is it incest to have sex with your sister even though you are not blood related but she's been your sister for ever since you were born. Many people will say yes that is disgusting and other will say if she's not blood related its no harm. Well I say that it shouldn't happen either way. What do you think about it.

No blood, no incest. But there are moral considerations to think about.

So...is she adopted?

I'd say yes, but if one has veiwed her as their sister for that many years then I dunno. I could see it if these were children sexualy expiramenting with on another (no REAL sex though, the "I'll show you mine if you show me yours" stuff.) then I see no harm.

To quote my insane PSO chat buddies-

"Incest is best put your sister to the test.":lol

But seriously, I think it's wrong... even adopted. Don't screw your family members(unless you're husband and wife or husband and husband or wife and wife, of course).

So all in all - No it is not incest as the word in it's dennotated meaning refers explicitly to blood relatives but to many people the connotation of the word would still be there because family is created in one's head more by status of the person as it apply's to your life more than blood.
Like Goten pointed out - one's husband or wife is part of their family although he or she is not related by blood simply because of his or her status in one's life - although the status does take into account that sex is OK with this person. Which is probably why the literal meaning of incest refers strictly to blood relation...
well that is my little opinion anyway.
My question is if one actually respects this person as his or her sister, then they would want to have sex with her would they? of course that goes into the question of respect for different status's of people in different situations and stuff.

so Ixzion probably summed it up best with saying that it mostly has to do with personal morals.

Well, is she hot?

*vomit*

Ok speaking of that why does she have to be hot? I mean she could be your sister and still hot.