Being the volcano groupie that I am, I've spent quite a bit of time studying the 79 AD eruption of Vesuvius. Pliny the Younger gives an eyewitness account of the eruption, which includes a description of the death of his uncle, Pliny the Elder.I'm with you Carl.
Until today, I never have heard of it being pronounced "ply knee." I've always heard it spoken as rhyming with Vinnie.
I mean, come on guys... Can you really hear some Italian guy saying, "Yo, Ply Knee!"
Shin, win, fin, thin. Logically, the pronunciation of Plin follows.
It's not spelled Pliney, after all.
And Vesuvius erupted on August 24th, which just happens to be my birthday. So I've spent a bit of time reading about it, too.