1. Deploy the field named “ Activity Subject” to your Leads Page Layout
  2. Create your Workflow Rule, using Activity Subject as the filter field, setting the value as desired
  3. Create a Workflow Action where type = Field Update
  4. NOTE: Anytime you are setting up a Field Update on the Owner field, make sure you are using the User ID, not the formal name of your user; For example, for user John Doe, insert this value 00530000000ibYc not "John Doe"
    1. To find a Salesforce User ID
      1. Go to Setup | Administration Setup > Manager Users > Users
      2. Click the User's name
      3. The ID is contained in the URL of the User detail page you are currently on and can be found in the browser address bar.
       
      Example: For URL "https://na1.salesforce.com/00530000000ibYc," the unique Salesforce User ID is: '00530000000ibYc.' This is the value you should use for setting a 'Record Owner' field or to transfer record ownership.