Lots of interesting things swirling around about SaaS lately, including the relationship to shared services within an organization. James Governer posted about the convergence of shared services and business process outsourcing, but I have a bit of a problem with comparing an internal mandated service with an external service about which you have a choice. As I said in my comment on James' post, the problem with equating shared services within an organization and a true outsourced SaaS is that an enterprise is usually captive to its shared services, whereas they have a choice with an external SaaS.
Imagine there was a delivery mechanism that allowed people to buy a single shot of Tabasco on-demand. Imagine there was a social mechanism that allowed people to share bottles of Tabasco (and many other flavours) with their neighbours.
Having seen these three posts in succession, I started thinking about the shared services analogy: similar to Veryard's SaaS one, except that your older brother owns all the bottles of hot sauce, and your mom makes you buy from him rather than the kid in the next block. If your brother's taste is the same as yours, that's great for you; if it's not, then he comes off like a bit of a tyrant. If you don't like his taste and choose not to have hot sauce, then he still justifies his existence because he's still the household standard, there's just less hot sauce used and your life is duller because of it.