Here are the different mechanisms to become a follower in OpenERP v7:

• the Follow button on documents
• you can invite partners to become followers of a document by clicking on the Invite button
• the creator of a document is automatically added in the followers
• the author of an incoming email (i.e. through the mail gateway) is automatically added as a follower of the related document, if the author is a known partner
• using the automatic creation checkbox in OpenChatter to reply to an unknown email address. For example, a lead is created because someone wrote to sales@yourdomain. The email address is not associated to a partner. When replying to the customer, there will be a checkbox asking you if you want to create a partner with this email address, that will be added as follower to the document, as shown on following figure
• in lead, opportunity, task, issue and recruitment, the responsible of the document (Salesman, Assigned To) is automatically added as follower
• following a sales team will make you follower of all lead associated with this sales team
• following a project will make you follower of all tasks or issues associated with this project