I think they're mostly tongue-in-cheek - and they all make me want to read on!
F
I quite like obscure off-kilter first lines, that you don't quite get at first.
On example I still remember, though it was from a chapter 1, not a prologue.
Vonnegaut (sp?) Slaughter House 5
'Billy Pilgrim was a spastic in time.'
You immediately have to stop for a second or two to try and make sense of it. Makes perfect sense ultimately though.
Darryl