Obviously this model fits much better with Microsoft's view of the software universe. Users gain the persistence and omnipresence of cloud computing, yet they keep buying traditional operating systems and applications.

One could argue that this is also the greatest weakness of the Live Mesh model, since Google offers its applications for free. But Microsoft is rapidly growing accustomed to competing with free software. Consider its recent Microsoft Equipt offering, which bundles Office 2007 with supplemental software on a subscription basis, priced for cost-conscious customers. For Microsoft, overcoming customer thriftiness may simply be a matter of adjusting its own licensing terms.

Google, by comparison, has a tougher row to hoe. Its Web-based applications are impressive achievements, but they lack the polish and functionality of desktop software such as Microsoft Office. Because of this, they are unlikely to win many converts among the "power users" who form Office's staunchest constituency. Plus, enterprise customers may be leery of the idea of storing and managing their documents primarily in the cloud, rather than on local drives.

In short, Google's approach to cloud computing is revolutionary, while Microsoft's is evolutionary. Live Mesh appeals to the status quo, which should make it the easier sell. And yet Google's momentum is undeniable.

For now, customers are free to decide which model better suits their individual workflows and requirements. Independent developers, on the other hand, face a more difficult choice. Do they follow Google's lead down the road of "pure" cloud computing, where both documents and applications exist solely in the cloud? Or do they take a cue from Microsoft and push data into the cloud, while still relying on traditional desktop applications to create and manage the data?

The SDK for Google App Engine is already available, and Microsoft promises to release an SDK for Live Mesh soon. For developers looking to push computing still further into the cloud, the question now is: Which cloud?