As I'm in the mood for finally responding to frequent requests, here is a list of case studies referring to SQL Server Data Mining on Microsoft.com.  Note that these are "marketing" case studies and are notoriously sparse on details, and that's aggravated by marketing focusing more on the relational engine than the data mining engine (in fact many of them refer to data mining without any details, but so is life).  In any case, you can use these whenever you get a response such as "but how do we know if SQL Server Data Mining is enterprise ready?" or "But does anyone like us use SQL Server Data Mining?" or similar questions.

Location Industry Case Study
Philippines Media & Entertainment Wireless Services Firm Doubles Response Rates with SQL Server 2005 Data Mining 10/23/05
Canada Professional Services Microsoft Partner Helps Internet-Monitoring Company Crawl 750 Million Pages Monthly 01/17/07
France Professional Services E-Commerce Provider Boosts Competitiveness with Microsoft Technology and Partnership 02/04/07
France Retail French Retailer Deploys Powerful Solution to Handle 1 Million Orders a Day 09/04/06
Israel Healthcare Microsoft SQL Server 2005 Data Mining Helps Clalit Preserve Health and Save Lives 11/03/05
France Manufacturing New Business Intelligence Solution Reduces Customer Churn by 25 to 30 Percent 03/16/06
United States Government The Illinois Department of Transportation Saves Lives with Microsoft Business Intelligence Solution 21-Apr-08
Germany Transportation & Logistics Global Air Freight Company Analyzes Mission Critical Logistics Data with SQL Server 2005 02/01/06
United Kingdom Media & Entertainment Scalable Data Warehouse Helps U.K. Lifestyle Group Consolidate Multiple Data Sources in Just Three Months 11/07/06
Italy Financial Services New Information System Increases Efficiency and Helps Double Profits at Italian Bank 02/16/07
United Kingdom Education Analytical Tools Help Research Group Provide New Insight Into How Darwin Developed His Theory of Evolution 11/07/06
United Kingdom Education Research Group Unlocks the Secrets of Darwinian Research with Mapping and Database Software 18-Mar-08
United States Manufacturing Xerox Develops Scalable, Hosted Solution to Optimize Global Print Fleet Management 11/11/05
United States Professional Services Database Products Help Real Estate Service Evaluate Millions of Homes Daily, Cut Costs 08/24/06
United States Financial Services Zurich in North American Anticipates U.S.$25 Million Gain with SQL Server 2005 Solution 01/22/07