Tom --
There are a lot of routes where they offer a substantial discount. The last time I was looking at them, they were running at $0.40 /mile, but the math hasn't changed that much at $0.51/mile.
Also, AAirpass gets you free drinks in coach, free headsets, and access to the AAdmiral's club.
The biggest reason to consider AAirpass though is the convenience. No ticketing and then refunding or changing tickets as plans change.