AOW looks confusing at first, but with a little explanation, you can get the info you need. AOW, <http://flyaow.com/classcwt.htm> is a great site to go to in order to get a pretty good idea of what the flight loads look like, and get a general idea of how many cheap seats are still availabl, but the information is not directly formatted. If you go to the site and then search for a flight, you will see something like the following next to specific flights:

Cabin class: F7 U0 Y7 S7 B7 M7 H7 Q7 L7 V7 K0 G0 T0

That shows you all of the classes of service available on that flight. Each class of service is a different fare for a seat. They start out with F & U class, both of which are first class. Then, the rest of the letters represent different coach classes (aka fares) in order of decreasing price and increasing restrictions. As a whole, that means that there are 7 or more seats still available to sell in F,Y,S,B,M,H,Q,L,and V class. You can not add them up to tell you how many seats are available, but you can see that that flight is not very full at all because Alaska is still selling pretty cheap seats (L & V class) etc. and has a lot more to sell. Alaska will never show more than 7 available in any class at any time.

On the other hand...
Cabin class: F0 U0 Y3 S2 B0 M0 H0 Q0 L0 V0 K0 G0 T0

This flight is obviously pretty full. Y is the most expensive coach seats and with only 3 of those, and 1 seat in S class, you can probably guess that the flight is already booked and these 3-5 leftover seats are only overbooking the flight. Remember... you can't simply add up numbers and assure yourself that 5 seats are available to sell. It does, however, give you a good idea of how many are left.

On a side note... U class is First class upgrades. So if you are trying to upgrade in advance, try to find a flight with those available.

Cheers!