From what I've been able to find from their (limited) site, AAirpass does seem to be a decent deal in certain circumstances. For instance: since you pay for tickets by miles used and not by actual fare, you can sometimes get into F on shorter distance flights for less than it would cost to buy the applicable YUP fare. After all, regular AAirpass tickets (and not the Miles Saver, or whatever they're called) book as Y fare codes, which can include YUP booking into A.

One example would be a trip from DCA->ORD. This would be a 1224 mile round trip, and would cost $1,398 to book as a YUP. With AAirpass, you'd use 1224 miles and book a YUP fare. Since AAirpass costs ~$0.40 per mile, that works out to $489.60 for the same ticket.

I think that's how it would work, but again, I don't think their site is too straightforward, so I could be wrong.