I thought one of the whole points of FFP's to begin with - when they were devised in 1980 or whenever - was to come up with an artificial currency that business travelers could accept without it being considered a kickback. It was an ingenius way to lure the employee - the one traveling - with something of value that he wouldn't have to give back to the actual payer of the travel (the employer, government, client, whatever).

If they were issuing cashback as a general practice, it'd either be considered an illegal kickback - or the payer would simply require the traveler to deduct it from the expense report. But miles are nebulous, which cleanses them for us to keep.

In short, the entire system is based on an ethical gray area - one that seems quaint today. But still, handling real cash somehow "makes it different". I don't really know why - I admit I'd be a bit hesitant to do it myself, yet I have no hesitation whatsoever accepting a Marriott Bonus Buck or a Hilton Free Night certificate - or any other bonuses an airline or hotel wants to throw at me.

What makes a Marriott Bonus Buck, with $100 or GBP100 clearly written on the front of it, any different than a Visa debit card? (Or, go one step further: what if the hotel slipped a crisp, genuine Benjamin under the door with your final bill?) I don't have a good, logical answer for that. Ethically, we like to stay arm's-length from anything that smells like a cash kickback, even though our miles, points, and certificates serve a very similar purpose.