Scott, I never get lucky enough to have too many spare seats beside me as I am a forward aisle seat pref and very rare to see too many spare seats (particularly on QF these days). Having said that, I had a spare sat next to me on a BNE/SYD flight a couple of weeks ago (never really thought about it, but it was a fullish flight, luck or design I don't know??).
On CX, BA or AA, I've never had the pleasure in Y to have spare seats beside me (except when I travelled J or F in the past couple of years, but that was more by low pax numbers in those classes than design). I have no trouble sleeping in any seat - little pills help me there. My flights on these OW partners aren't that many in the past year - 3 sectors for CX (2F, 1Y), 7 with BA (1F, 5J & 1WT+) and 8 for AA [6F (if you can call it that!), 2Y] - so I'd hardly say my experience is much to go by.
