Sharing saves resources, but also poses a few issues. Sometimes an single individual hogs the resource (the roommate who drank all the milk) or tries to profit off the joint labor that created it. Since sharing is a collective endeavor, it can pressure 'Us vs. Them' models considerably. This cultural disruption can be threatening - Hp, for example, sensing that sharing would cut into their profit margins, declared a war on sharing in 2002.
Be that as it may, sharing is everywhere in IT and is only going to increase. Most businesses already share networks, databases, servers because it simply makes sense - it would be silly for each user to have their own network, just as it would be silly for each automobile owner to have their own roads. Only the desktop PC, the proverbial car of the information superhighway, has not fallen into the shared realm.
But all that is changing rapidly. As resources draw scarce, IT sharing is going mainstream. With drastic budgetary reductions and the drive towards efficiency, CIOs are now looking to implement any technology that improves efficiency. And the solution is sharing - Virtualization is being used to share servers, and the shared desktop is here. At a larger scale, extranets, software as a service, and industry consolidation will continue, maybe until there are only five shared computers left in the world. When we get to that level of efficiency, we will have sustainable IT. And that's a party.