I got matched on an in progress queue for DD the other day where they'd already rushed through the first hallway, killed everything and quit. Total waste of half an hour DPS queue. And I never queue in progress as tank, because it means the previous tank either quit or got kicked, which are usually pretty good indicators of a failgroup.

Only time I ever queue for in progress is CT raids when I'm only in it for the weekly, or if it's WOD and I don't need anything from the first bosses on that class.