I used a clear plastic CTC bag when I came back from PBP in 2011 but, having finished the ride, I really didn't care whether the bike ended up being smashed into tiny pieces.
(I'd also like to think that it was French baggage handlers and they might be quite careful with un vélo.)
Some argue that they might be a lot more careful with a bike they can see, in a clear plastic bag, than a bike they can't see in a generic soft case. But this is highly dependent on the individual baggage handler than ends up handling the baggage.
In my example it survived with no problems.
I used a load of pipe lagging and zip ties plus some PBP signage in order to make it a bit more secure.
[EDIT] Digs out a photo...