One of the useful additions to Act! was the automatic "Last Reach", "Last Attempt", "Last Letter" etc System generated fields.
What would be really useful would be the ability to define new fields like these based on User Defined Activities.
So, for example, a customer wants to differentiate between a standard Meeting and a user defined "Maintenance Visit", they could schedule a "Maintenance Visit" for their engineer in the Calendar and, when Cleared, the system would automatically generate a date in the "Last Maintenance Visit" field. This field could then be available to Lookups or, indeed, Smart Tasks to better manage customer service.