A composer/artist who might deserve consideration for using the vernacular
effectively in classical music is Edgar Meyer.  I think he illustrates the
difference between what Steve is talking about and the smarmy crossover
stuff that most of us disdain.

I've been listening to his String Quintet.  It is clearly classical
in constrcution.  Yet the strains of Appalachia are never far from the
language.  In fact, based on something I learned last week from Mimi, it
represents a circle being closed neatly.  According to her, the Appalachian
fiddle sound with which we are familiar as a vernacular voice derived from
Scotch Irish immigrants trying to simulate the folk music of their native
lands on inadequate stringed instruments.  Now we get Meyer reintegrating
that sound into a classical form we associate with Europe.

I think that much of third stream jazz-classical fusion tries too hard
and ends up sounding neither like good jazz nor good classical music.
However, increasingly one hears young musicians who don't worry as much
about label and in their work provide comfortable blends of vernacular
language into constructions that merit consideration as serious are music.
One recent example that comes to my mind is the collaboration of pianist
Kenny Barron and violinist Regina Carter.  She is classically trained.
Their composition Freefall on the eponymously named CD seems to me to
belong on the same shelf as my Bartok sonatas.

By the way, two other American composers I would nominate for using the
vernacular in their classical compositions (though both also composed
popular music as well) are Merideth Wilson and Robert Russell Bennett.

Ed