Following this thread with interest. I sometimes fly with an acoustic parlor guitar in a gig bag that's small enough to fit in overhead bins.
I've heard of some people putting basses in a gig bag and then into a hardshell golfclub case (I've seen some sturdy-looking SKBs). I'm not sure of the dimensions of these, and I don't know if large-bodied basses would fit but AFAIK most US airlines let you check two pieces of luggage and a golf case (how's that for catering to the needs of rich old white guys?

) for no extra charge. I don't know if the SKB Bass Safe would pass for a golf case.