Microsoft has released 64-bit Office 2010, at least to MSDN and Technet subscribers, with general availability to follow shortly. Now that 64-bit Windows is commonplace, you would think that 64-bit Office is the obvious choice.

Apparently not. Take a read of this technical note before installing 64-bit Office 2010. In essence, it recommends installing 32-bit Office, even on 64-bit systems, except in the following case:

If some users in your organization are Excel expert users who work with Excel spreadsheets that are larger than 2 gigabytes (GB), they can install the 64-bit edition of Office 2010. In addition, if you have in-house solution developers, we recommend that those developers have access to the 64-bit edition of Office 2010 so that they can test and update your in-house solutions on the 64-bit edition of Office 2010.

That’s a small niche. So what can go wrong if you decide to go 64-bit? First, it might not install:

If 32-bit Office applications are installed on a computer, a 64-bit Office 2010 installation is blocked by default.

says the tech note. In addition, if you manage to install it, you will have problems with 32-bit Access applications, 32-bit ActiveX controls and COM add-ins, in-place activation of documents where the OLE server is 32-bit, and VBA code that calls the Windows API. VBA deliberately disables API calls defined with the Declare statement; they must the updated with a PtrSafe attribute before they will run.

The Office install DVD includes both 32-bit and 64-bit versions, and the 32-bit version installs by default irrespective of the version of Windows.

Of course I will be trying 64-bit Office on a spare machine. I’m interested to know, for example, whether Outlook benefits from all that extra RAM, since it is notoriously slow. But overall, 64-bit Office 2010 looks more like a release to prepare the ground for the future, than one for normal use.