When you stop a project collection in TFS 2010, it asks you to enter a reason why you are stopping that collection:
This text will be displayed to the users when they try to use an artifact in any of the projects in that project collection:
Note that this only affects those artifacts that are managed by TFS (work items, builds and source control items). Users can continue accessing the reports (handled by SSRS and SSAS) and documents (handled by SharePoint).
This is a minor feature but can be very useful when you need to service the project collection. It is still a good idea to make the users aware of the servicing plans in advance though!
Originally posted by Mehran Nikoo on 15th June here http://mnikoo.net/2010/06/15/providing-a-reason-for-stopping-project-collections-in-tfs-2010/