Domestically, it is allowed. Since I don't get upgraded all of the time and would be in the first few economy rows otherwise, if it is not being used, I'll go up past the curtain.

Since AA is rather unique in this policy, it is an "only those in the know" situation. You are allowed to queue behind the curtain if needed. I get it that F passengers don't like the situation, but I've decided the airline has made the decision of access (and reinforced it after the merger). If someone feels that lowers the F experience, they are welcome to pick another carrier.

Rasheed