1) ASSERT: have an OpenShift Express account
2) EXECUTE: launch the OpenShift Express application wizard, enter your credentials and get to the Application selection page
3) EXECUTE: you get informed that you have to enter a domain name: enter some name
Result:
The error marker disappears, you cannot see any information/error that would tell you that you have no domain yet
This is not really harsh (since you still cannot switch the page, you'd be able to only if you had selected an app and you can only have apps if you have a domain), but it's not really completely intuitive.