Another vote for Yes.. but it is only worth it if you are planning on international travel or using miles/evips to upgrade.

It was invaluable in planning a recent trip, where I secured upgrades on the return and got waitlisted for outbound. I set an alert, and got notified today about 1 (out of 2) C seat available. Called AA, split the PNRs and got my companion upgraded. Now, its just me waitlisted, which I am considering an almost sure thing from reading people's experiences.

However, I dont use it for domestic travel and its not even worth it for that.