I speak with an RP accent* (see voices of a.org), and I must confess that I do immediately assume people who speak in the vernacular as less intellegent, but it doesn't take long for that illusion to be dispelled after speaking with someone if they are actually very bright!
If I hear a girl speaking with a german accent, I find it very sexy... I don't know if that relevant to this disscusion. :-)
*my accent is a bit of a mess now, living in London for 8 years has push me into what commonly known as estery, that coupled with living with a Canadian girl friend for 6 years has added a slight north American twinge to it.