At least one FTer reported that s/he DID receive both bonuses simultaneously. I signed up for both earlier this year, but I don't actually know whether I received 2x, 3x, or more.

But if you pay close attention to the way the promotions are structured, you'll notice that, if the two bonuses were to be cumulative, you still would not receive 5x. For "always double miles" purchases, you'd get no additional bonus for the 2x promotion, and 1 Skymile per dollar bonus for the 3x promotion. So for these purchases, even stacked promotions would be the same as just the 3x promotion alone.

For other purchases, you'd get 1 bonus Skymile per dollar on the 2x promotion and 2 bonus miles per dollar on the 3x promotion, for a total of "only" 4 Skymiles per dollar spent.

So the most you could get (if the promotions did stack) would be 4x, and paradoxically, you'd actually get more miles for non-favored purchases like at Wal-Mart than for the supposedly favored "always double miles" purchases like at gas stations and grocery stores.