Software as a service (SAAS) is a both a technology and a [partial] business model. Companies are looking to outsource expensive servers and related IT services by renting processing power from companies like Salesforce.com and Amazon. Directories exist to help you find such services: http://www.saas-showplace.com/saasindustrysector.html

Significant interest and usage of SAAS is underway:
http://www.cio.com/article/109706/The_Truth_About_Software_as_a_Service_SaaS_

The primary advantage of SAAS, as quoted in the CIO article above:

The prime reasons for a CIO to consider SaaS are its faster deployment times, its lack of up-front license and infrastructure costs, and its ability to address vanilla business processes so you can focus your resources on custom processes that make a real difference, says Accenture’s Modruson.

But what happens when your rented service quits working? That's what happened to Amazon's S3 service on Friday, February 15: http://www.cio.com/article/184451/Amazon_s_S_Down_for_Several_Hours

Getting this remedied -- if possible at all -- is a bit more complicated than calling your landlord and telling him that the septic tank is backed up. One Amazon customer said, "It's becoming very embarrassing for us here," one wrote. "We desperately need an update... it's a huge hit on our reputation."

My point here is not that SAAS is evil. In some sectors -- particularly for generic, commodity software features -- it makes perfect sense. The point is that companies need to control their data, no matter where they decide to put it. Making plans for your own internal server's downtime is smart business. Making plans for the outtage of an outsourced server (or entire application) is just as prudent.