We have just released a comprehensive Purchase Order Approval System for ServiceDesk Plus On-Demand. These include a ‘multistage, multiple approver’ approval mechanism for Purchase Orders(PO) as well as the ability to add Invoice Details and Payment Details to a PO. 

Please find details of this and other updates at   http://ondemand.manageengine.com/service-desk/whats-new.html

As always, this update was' In Service' with zero downtime of the application.