One of the critical success factors of SaaS is the paradox of confidence.
As I've pointed out here before, SaaS (Software-as-a-Service) helps you to manage your Service-Oriented Cashflow. By shifting from fixed costs upfront to variable costs later, you may be getting a cashflow advantage even if you end up paying more in total.
Now here's the thing about confidence. Optimists prefer fixed costs because they expect to get economies of scale; pessimists prefer variable costs because they fear they might not. So in an economic downturn, it makes sense for pessimists to shift a lot of expenditure to Pay-As-You-Go.
Some analysts are comparing SaaS (Software-as-a-Service) with ASP (application service provision). Although ASP had some notable successes, it wasn't anything like as commercially successful as its champions hoped. However, in times of credit crunch and pessimism, the cashflow arguments may be much more telling this time around.
Now here's the second thing about confidence. Pay-As-You-Go may improve the cashflow for the service consumer, but it typically causes cashflow problems for the service provider. So maybe only the most confident service providers - with the best technology and the most confident investors - can afford to offer services on a Pay-As-You-Go basis.
And here's the third thing about confidence. The consumer needs to be confident that the service provider is going to stick around. That means financial stability as well as technical stability. Does this mean it's the big companies who are going to make all the money from SaaS?
Microsoft certainly hopes that "Customers will write us bigger checks". See comment by Ed Brill (IBM), via Esther Schindler. But Microsoft can probably afford to wait for the cheques to roll in. Smaller companies will somehow have to find a way to finesse the cashflow.