Hello,
Actually, we never suggested any particular
RoR application to our clients as it is a third party product.
Just checked some blogs and developer reviews about
Twitter and found many fans of this application
Twitter is the biggest Rails site on the net right now.
Twitter developers believe in
RoR and they've noted that it is a great tool for development and rapid prototyping. It also takes less resources so you can use many instances at a time smoothly.
So my vote also goes to
Twitter