To find out what stairs you can currently challenge someone in, first go to the Main Stairs Page, then click on "Show your stairs only" link. The ones in BOLD are ones you can make a challenge in. .
Take for instance Standard Stairs (Backgammon). There are currently 2 steps. Is there a way to see ALL of the players on step 1 AND step 2? Rignt now, you can either see both steps, or see every one on step 1. Or will the problem become moot once everyone starts getting onto more steps?