It seems like the shift to 64-bit may take a bit longer than expected. Microsoft has been slowly migrating from 32-bit to 64-bit with its operating systems, Exchange Server, and now with Office 2010, its applications. All is not great Wonderland, however. Microsoft itself has recommended that users not upgrade to the 64-bit version if they use Office add-ons.

I have been using the 64-bit version of Office 2010 for some time now, and have had no issues with any of the applications. I do not use many add-ons, though.

This quote came from the Microsoft Office 2010 Technology Guarantee FAQ page.

Yes, 64-bit Office 2010 product upgrades will be available. However we strongly recommend most users install 32-bit version of Office 2010 on both 32 and 64-bit Operating Systems because currently many common add-ins for Office will not function in the 64-bit edition. The 64-bit installation of Microsoft Office 2010 products will be available for users who commonly use very large documents or data set and need Excel 2010 programs to access greater than 2GB of memory. There may be technical issues with the 64-bit version and in order to install a 64-bit version of Office 2010 product users must have a 64-bit supported operating system on their PC.