Be Sure To Link Your Activities To The Correct Module.
(...Accounts, Contacts or Potentials)
Assigning or Linking your activities correctly ensures they will display under the correct Customer or Deal they pertain to.
You can view these activities under Views or Reports.
If you don't Link or Assign activities correctly, you will have orphaned activities, decipherable by Subject only. Thus, reports for sales activities/effort, cost of sales, and customer activity will all be skewed.