I think the red-eye SEA-IAH is like channa's SMF flights.

I've seen empty seats in F and have been EUAed all six times I've flown the flight in the last 15 months (5 @ 5-day, 1 @ 3-day).

BTW, so far in 2006 this Plat has been upgraded on 24 of 28 mainline flights.
The four that weren't; (and fare class):

EWR-FLL (L), EWR-DFW (X), EWR-IAH (L), and SFO-IAH (H).