"not for nothing?"

Anyone know the meaning of the phrase "not for nothing?" It seems to be generally used to mean the opposite. Help?

Whenever you see the phrase "not for nothing" substitute the following phrase--"If you don't mind my asking" and it will make sense.

In certain parts of NYC you will hear it as "not for nuttin" as in "Not for nuttin Tony but how the hell did you get this job".

And you will never hear the -ing, it is almost always pronounced "not for nothin".