Customers sometimes need a good way to bulk edit data in CRM.
One solution is to export the data, adjust it outside of CRM in a tool like Excel, then re-import it.
You can get an ms crm import tool from http://mscrmimport.codeplex.com/ (read about it at http://blogs.msdn.com/b/crm/archive/2008/01/25/data-manipulation-tool.aspx )
A more powerful and user friendly Excel editing tool is EBAX: http://www.mscrmexcel.com/
In general I think EBAX is a good compromise of raw editing-in-Excel power and CRM's use-our-web-services restrictions, so I recommend it particularly to clients who have a few users who need some powerful or bulk access.
The only consideration I’m aware of for a bulk editing tool in a deployment is that it’s important to train both the power users and developers that fields which were disabled via Javascript aren’t really disabled – users should avoid editing a custom calculated total field, and developers should avoid expecting a user to be unable to edit a custom calculated total field simply because it was disabled on the web form.