I also ran into an issue involving a conflict between a 64-bit installation of Office and a 32-bit version. Microsoft says an Office 365 license can cover a mix of 32- and 64-bit installations, but if you're upgrading from Office 2010, you cannot switch from the version of that installation. In other words, you can't upgrade the 32-bit version of Office 2010 to the 64-bit version of Office 365 and vice versa. If you don't have a previous version of Office installed, you can choose either version, but unless you frequently work with large data sets, Microsoft recommends using the 32-bit version, even if you're running a 64-bit version of Windows.
The cloud-connected Office 365 is potentially a game changer for Microsoft's Office franchise. In its current incarnation, however, Office on Demand doesn't offer the type of flexibility and consistency you'd hope for with a Web-friendly version of Office. We are also still eagerly awaiting versions of Office that will work with an Android tablet and an iPad mini; be sure to read more about the many faces of Office, including details about what you can and can't get on mobile devices.