Setup custom roles so that cases are auto assigned to the user creating them.

In order for the 'Assigned To' field on cases to default to the user creating the case the role must be setup accordingly:

Go to Setup > Users/Roles > Manage Roles > select requested Role and click Customize > new page pops up with selected role

1. Employee Restrictions' must be set to one of the following:
        a. 'None - Default to Own'
        b. 'Own and Subordinates Only' 
        c. 'Own, Subordinates and Unassigned'.
2. Main/Top section of Role > Support Role = TRUE

Note: The user creating the case must also be marked off as a Support Rep (Employee Record > Human Resources tab > Support Rep = TRUE).