I was in the B17 a few times. I figured since no one was using it, and several times when I spawned at the base there were no other vehicles to be had, that I'd take the B17 for transport since its quicker then walking.
If there were no friendlies around my intended destination, I'd put down a stick of bombs or two and and then bail out. I got a few kills that way and was able to get back to the front quicker.
I trust this didn't interfere with anyone else? I think in the right situation the B17 could be useful. If nothing else, it will force the opposition to put a few guys in anti air guns (making them static targets), draw some attention away from Zorro and other pilots. Placing a string of bombs across one of the bad guys "mass spawns" would be an effective tactic. :)
If we can develop tactics were one or a few people can tie up a larger number of guys on the other side from their primary objective, this gives us an advantage. Thats why I'm a fan of base infiltration.