"not for nothing, but"

[Geoffrey Nunberg]

I had a note from a journalist I know asking me about the use of "not
for nothing, but" to mean something like "No offense, but..." In this
use it doesn't trigger inversion:

"Not for nothing, Baby Ghost," who graduated from SUNY-Albany, "but
it took you four tries to spell Ronkonkoma." (NY Daily News)

"Not for nothing," Sadik said, "but there's a lot of women who lay in
bed and think about Furio." (NY Daily News)

"Not for nothing," said a size large salesman, pointing at his dining
companion with a fork, "but this mutt contractor is killing me. I
gotta get some relief." (NY Times)

All Mayor Mike can say to the Iraqis is, Not for nothing, but if
yooze ever walk your Rottweiler through Powderhouse Park and it
growls at me, put up your dukes, pal. (Boston Herald)

In a Nexis search, the cites for this use of the phrase seem to occur
almost exclusively in Northeastern papers (and almost always in
recorded speech). I've never heard it used myself, not having lived
in that part of the world for 20 years now. Does anyone happen to
know the dialectology of this one?

Geoff Nunberg