Hi Rhonda -
Here is the issue with Clean. It will update and clean accounts. It will not update leads.
If you want to update leads, you need to purchase the prospector license. That is the one where you pay for each indvidual. Only if the individual exists in the Data.com/Jigsaw database, will the lead record be updated. Regardless if the company exists in the database.
Example, Joe Smith comes in as a lead from Nordstrom. Joe doesn't exist in the Data.com/Jigsaw database, however Nordstrom as an account does. Data.com clean will not update the prospect recrod, but it will update the account.
A bit frustrating.
One of the tools that I've used several times for backend data append is Insideview. It will append all sorts of information to the lead or contact record.
I would seriously consider looking at Insideview for Marketing (they are on launch point too) before moving forward with clean.