Zune 4.7 PC client is the vehicle via which Microsoft will deliver operating system and app updates to Zune media-player and Windows Phone 7 customers. However, a number of users -- most of which seemed to be running 64-bit Win7 reporting memory-usage problems.
One Microsoft representative requested those experiencing problems to send their Zune database files to him for further investigation. He explained that the database file is located under C:\Users\<username>\AppData\Local\Microsoft\Zune\ZuneStore.sdf (assuming you are using Vista or above and your system is located on C:). "Or you can use %LOCALAPPDATA%\Microsoft\Zune\ZuneStore.sdf," he said.
Chris Woodruff notes there also is a media-collection reset tool which may fix users' memory issues with Zune 4.7.
Download: Zune media collection reset tool