You can use the import wizard to erase existing field values.
Once a custom field is deleted, can it be restored?

Which of the following make a User record Unique?

Custom Summary Formulas are:

At Universal Containers, there is a custom field on the Lead named Product_Category_c. Management would like this information to be part of the opportunity upon lead conversion.
What action should the administrator take to satisfy the request?

Can the User Records be permanently deleted from the Salesforce.com?