Laptop attached via straps in slip case will turn it into 'one bag' to keep airlines sufficiently happy. Its its 'attached' and you can carry it in one hand as a bag, they dont' seem to care. Weight of coruse, is a different problem.
Also, laptop in a simple slipcase will fit in inside pocket of Domke Photo Vest just fine. (I use a 13" laptop, but a 15 also fits, just a bit heavy).
I fly across the world a fair bit, and nowdays NEVER travel without wearing my photo-vest, it is a godsend for so many reasons. Dosn't matter if its a phot trip, or business (though normally I always carry camera gear).
I've been eyeing off the Kiboko for some time. I currently use a thinktank Airport international, which is good, but I think the Kiboko could be even better for being both travel, and shooting backpack.
Regards
Mark.