has anybody had any experience with using this program in a business?
Is there some context to this question? Are you going to start a business using Windows Defender to search for Spyware or something? Windows Defender shipped inbox with Windows Vista, and is available as a separate download for Windows XP. Works fine for spyware and is not an Antivirus program.
It is not a managed solution in case you need reporting at the business level, that's where you'd want to go with a commercial solution from Symantec or McAfee or with the Microsoft ForeFront line of products (which are focused at the Enterprise and do offer all of the centralized monitoring/reporting you would want in an enterprise environment).