We discussed the shared database approach or multi-tenant data layer and came to the conclusion that running backups is not so much of a problem but restoring data on a tenant by tenant basis would be a complex pattern that is not supported currently, neither by software vendors nor by the Windows-or .NET platform.  I recognize that there are scenarios where sharing the same database can lead into scalability advantages. This would be the case where database size is so small that the overhead of running the system vs. the actual tenant data limits scalability. This is a scenario that is very likely to exist in consumer oriented hosting solutions. Nevertheless as there is no solution to the backup and restore scenario and other parts of the platform seem also not ready -  I would not recommend this scenario to a Hoster or to an ISV.