If accessing a customer's data in CM-A, and then you use the "AR" link to go to AR-C, after you come back to CM-A you can't clear the screen to work on another Contact unless you exit the menu and come back in again. Does anyone else find this as bothersome as me?

Requiring the addition of Default Terms, Charge Interest, Send Statements, and Tax Group would be good.
 
Bigger request, sorta related. Make CM-A and AR-A much more tightly integrated. At the very least, when you make a change to one that has a corresponding field in the other, ask "Do you want to duplicate the change in [the other one]?" Better yet, just have it make the change, or let the user define whether they want it automatic or not.
 
BTW, I like having the AR button available in CM-A. Why not integrate the ability of Evo to show the AR-A info without the ability to change it (again, user-defined selection).

One thing to note: you can use <PgUp> to switch from one to the other as well, so you'd have to eliminate that too...