Often times, before server reboots in windows server 2008 you will want to verify that there are no open files. This is because if the server is rebooted while files are open there may be some data loss. Data loss is something that should be avoided.
To view the number of open files navigate to the following location in windows server 2008
Start -> Administrative Tools -> Share Storage Management
You can then view the number of open files, and contact the appropriate users to have them close it.