Tom Berquist the CFO of Ingres recently had a post on "On-Demand" Applications. Check it out here:

Some excerpts from the post:

Salesforce.com doesn't have an order management system or a backend financial system. After a fair bit of analysis we selected Intacct and are now in the process of implementing it. One of the biggest factors in our decision making process was its integration with Salesforce.com. Opportunities that our sales force enters in Salesforce.com can be converted into orders and invoices in Intacct and the entire financial history can be viewed in Salesforce without dealing with login details. This is done without any data integration!

During the B2B madness of the late 1990's, I covered Ariba, Commerce One, i2 Technologies, and many others that were trying to build B2B infrastructure that integrated through complex data translation procedures. These methods proved to be too expensive to implement. The new way that Salesforce and Intacct solved the problem is by using HTML and other web browser based technologies that "fake" the integration. We hope to be live with the solution in September and I will update you on what we learn.

Source: 1

Prashanth Rai