The lead association with tasks and appointments should not be separate from those in the address book. There are two reasons for this:
I will convert leads into the address book and I want to tasks and appointments to remain associated with the new contact.
I may have meetings (appointments) with both leads and address book entries. How do I configure a meeting with a lead who is an employee of an existing customer in the address book?
Currently when a lead is uploaded we lose the link between contact/lead and activity.
Curtis Barranoik commented
In addition to this, provide the ability to search leads in the Outlook add-in in order to link incoming/outgoing emails to leads.