This has been a concern to me too. I have a Citibank Cash Rewards card that gives me 5% cash back at supermarkets, gas stations, and drug stores. Since they sell AA gift cards at many supermarkets, this would essentially be a nice discount!

I've already done this with Best Buy, Nordstrom, and several restaurant gift cards... enough to max out my $300 cash back limit last year. But I'd be hesitant to lose the coverages provided by most credit cards on something like an airline ticket.