I added in codeplex the tool Excel to Dynamics CRM, it's a beta version.
Excel to Dynamics CRM for Microsoft Dynamics CRM 2011 makes it easier for the CRM users to upsert (update and/or insert) data from an Excel file.
The tool will analyse if the data in the Excel file are correct or not.
And if the data are correct, the tool will update the records in CRM if he can match the excel line with an existing record, or he will create a new line.
I recommend to use the existing import feature of Dynamics CRM 2011, but in some specific case, this tools can be help you.
You can find more infor and download this Tools at this address :