Using a wildcard inclusion managed path at the root of a web application in SharePoint Foundation 2010 or in SharePoint Server 2010 is not supported. This configuration is not explicitly blocked by the user interface or the command line tools, however there are several features in the products which will not work properly in this configuration.
This configuration is not supported even if the web application is using classic Windows authentication and will not use claims authentication in the future.
It is not supported to in-place upgrade a WSS 3.0 or MOSS 2007 farm which has a root wildcard inclusion managed path, however this is not explicitly blocked. It is advised to resolve this problem before attempting the upgrade. It is not supported to upgrade a WSS 3.0 or MOSS 2007 content database using the database attach method which was using a root wildcard inclusion managed path, although this is not explicitly blocked by the product.
The recommended methods to restructure site collections created with a root wildcard inclusion managed path are the following:
1. If the number of site collections is less than 21, then add an explicit managed path for each site collection created at the root. More information about the supported managed path limit can be found at http://technet.microsoft.com/en-us/library/cc262787.aspx#WebApplication
2. Move site collections to a non-root level wildcard inclusion such as /sites/ using site collection backup and restore. For more information visit http://technet.microsoft.com/en-us/library/cc706871(office.12).aspx and http://technet.microsoft.com/en-us/library/ee748609.aspx
Note: If using the site collection backup and restore method to refactor the "My Sites" in a farm, like any "My Site" rename event, additional work may be required to fix-up the user profile and Active Directory entries for the "My Site" along with any offline links to the "My Site".