Personally I think you're better off with earning 1 tax-free AA mile +.05% interest than the low offers out there today on liquid accounts.
On $10,000 in a back earning 1.1% you'll earn $110 in a year. Less say 30% in federal, state, local taxes, etc. leaves you with $77.
Or you can earn 12,000 miles and $5 interest.
So $77 in an ING account or 12K AA miles + $5 in a Bank Direct account.