Although free software may never be widespread, when Salesforce.com opened the pricing door a crack with a model different from the standard perpetual-license model -- with its huge up-front costs -- customers rushed in and flung the door wide open.

The slow and steady transition to SaaS (software as a service) gives the enterprise something else it wants and needs: a fairly stable budget item. The per-user, per-month pricing model is a fixed cost. As such, it allows a company to predict what its expenses are going to be, says Tim Bajarin, chief analyst at Creative Strategies.

Companies are also looking for more flexibility. During the past six months, there appears to be a slow but not imperceptible movement toward other deployment models, accompanied by other pricing models.

The pure utility model, for example, is back, with fees based on actual use of processing power or disk storage. Why should companies that need to crunch numbers just once a quarter have to invest in expensive BI solutions when they can pay by the compute cycle?

Mark Clayman, CIO of application management provider NaviSite, believes the possibility for a company to try things out without making large capital investments is driving the uptake of the SaaS model and its many permutations. There always seem to be small- and medium-size short-duration projects; what could be better than adding the capacity -- and even the application itself --- on an ad hoc basis? This model can be attractive even if it is just to do a beta test of an idea, Clayman says.