Another client of mine was hit by this recently; the issue of improperly using the Notes Tab. We had found that an end-user was completing calls using the tab (instead of properly using Complete from the top level menu). To be sure, the Notes tab is handy but should be used for general “non-transactional” items. Like driving directions, shipping instructions, etc. You will also run into eventual issues exporting data from the Notes tab should you ever choose to go to a different CRM product.
Here are a few ways to mitigate your Notes Tab issues;
1. Make sure that end users understand the difference between Notes and History.
2. Turn the Notes tab off for everyone under Tools | Users Settings | Preferences | Record | Tabs.
3. Place some easy-to-use Complete a Call buttons on the tool bar using the toolbar designer (Add/Remove Buttons | Customize | Commands | Complete).
Again, use the Notes tab sparingly and with caution. And good luck!