Pinpointe supports a single user ID (login ID) per customer. This differs from services such as Salesforce.com where you can purchase separate user IDs for your corporate account. By default, your Pinpointe user ID (login) will be created using your email address. Multiple people within your company can share this single user ID - however, two people should not edit the same campaign simultaneously.
Enterprise customers sending more than 250,000 emails per month can get a dedicated instance of Pinpointe, which will allow your company to create multiple user logins with separate access profiles (e.g. restrict some users to only access lists, and restrict others to only be able to send emails, etc) for users and/or departments.