When I convert a lead to a contact, where does the source field go? Does this mean I can't view all contacts added by a certain user?
The source field is not carried over from leads to contacts upon conversion. Because of this there is no default functionality to view all of the contacts added by a certain user. The suggested workaround is creating a new custom field for leads to store the value from the source field. You can then set it up to be transferred to the contact upon conversion.
For more information, see this article: Converting leads.