I built my SaaS application using Rails & decided to have a separate PostgreSQL schema for each customer's data. It seemed a neater option to me rather than putting account_id kind of field in all of the tables. Also, having a full fledged database for each customer was an overkill for my application.

You can refer these resources:

Architecture Strategies for Catching the Long Tail - http://msdn.microsoft.com/en-us/library/aa479069.aspx

Multi-Tenant Data Architecture - http://msdn.microsoft.com/en-us/library/aa479086.aspx

p.s. I am also based near Delhi. Feel free to connect with me if you would like to discuss anything in detail.