Leads - Do Not Create Opportunity option
When using the Leads module you can Convert the entry to an Address Book entry.
When doing so you are presented the option to create an Opportunity at the same time. There is also the check box available for 'Do Not Create Opportunity'.
However, there is no option to enable this checkbox by default. This would be useful if you are a business that either doesn't use the Opportunity module, or creates Opportunities manually at a later time.