"Not for nothing..." new meaning?

[Douglas G. Wilson]

>I have lately observed the expression "not for nothing" used at the
>beginning of a personal observation to mean something on the order of: "I
>really don't want to say this but I feel I need to", as in:
>
>"Not for nothing, but I think you've been wound a little tight lately."
>Paulie "Walnuts" to Tony Soprano (Season 3, Episode 13, 20 May 2001).
>
>And some Googled examples:
>
>"Not for nothing, but look who's calling someone a pig." (4 Sept 2002)
>
>"Not for nothing, but you D.C. motherf***ers couldn't keep a secret if
>someone had a gun to your heads." (New York City, 15 March 2002)
>
>"Not-For-Nothing But...If at anytime you don't like what your reading, then
>close your eyes!" (Dudley, Massachusetts, 29 April 2002)
>
>Has anyone observed this new (to me) usage outside of the northeast? And any
>earlier observances of it? I hear it more and more frequently in speech
>originating around New York City, and have only started noticing it in
>print, but it's one of those things that--now I am aware of it--pops up
>everywhere.

I have never heard this and a brief canvass of a few acquaintances here in
Pittsburgh turns up utter blanks.

I find it on the Internet from the early 1990's, mostly in the Northeast at
a glance.

It is utterly opaque to me; I am flummoxed.

It's usually "not for nothing BUT" and in some cases it seems to have a
mild interpretation like "excuse me but", other times stronger like "I hate
to be so rude but".

Is the expression supposed to have a double-negative sense as in "it's not
worth nothing" or is it two negatives make a positive as in "it's not
without value"?

-- Doug Wilson