We have our contacts assigned to various sales consultants. Consultants are only permitted to see and interact with their own assigned clients. However, with the features promoted in Pro Plus, there are drop-down menus that allow a consultant to see opportunities, campaigns and email templates associated with other salespeople. Additionally, once you have accessed the other person's contact through the opportunity tracker, you can open up all the email dialogue between the contact and the other salesperson, effectively eliminating any sort of privacy that exists from creating different users in the first place.
