Being a Saturday morning, I’m not on any official cases – however, in a tweet by Bil Simser earlier today I learned something rather disturbing that I thought should warrant a reference in my case files:
bsimser RT @sondergaard: Edit in Datasheet view not possible with Office 2010 x64 http://bit.ly/dD8aFI {among other x64 client restrictions}
Uh-oh. I followed over to Ishai Sagi’s blog post from yesterday and learned the awful details:
I installed Office x64 - in hope that it would work better on my Windows 2008r2 machine, utilizing whatever it needed from its 12GB RAM (ok, honestly - I don't actually need 64bit office. this version is meant for excel dark wizards who need more power when working on worksheets bigger than 2GB). However, I almost immediately regretted that choice, as now I cannot use the datasheet view in SharePoint (both 2007 and 2010). This technet article explains that this is because the 64bit version does not support the 32bit activeX that is used by the datasheet view:
"The Edit in Datasheet view functionality is not supported if you install 64-bit Office 2010. However, the functionality is available if you install 32-bit Office 2010. "
Definitely a caveat emptor for your deployments – and rather ironic considering how, for example, Adobe has been given the gears for not having a 64–bit version of Flash available and similarly emploring users to do the 32–bit hokey-pokey. Diving in to the referenced TechNet Article (64–Bit Editions of Office 2010), there is a downloadable poster that outlines the deployment considerations you may need to be aware of when considering a 64x Office 2010 install – see the following capture:

Highlights:
Advantages – more memory, Excel 2010 can have larger workbooks, Project 2010 can have larger projects (which, if you need it, suggests that technology isn’t your problem) and “enhanced default security protections”.
Disadvantages – 32–bit Access databases can’t be migrated directly to Office 2010 64x; 32–bit Active-X controls, COM Add-ins will not work; in-place activation of 32–bit components will likely fail; due to a lack of 64–bit Intel MMX support, GDI graphics rendering will be impacted; VBA code that uses the “Declare” statement to access Win32 API functions will need to be revised to use the PtrSafe attribute.
Something to bear in mind as you advise customers on migrating to SharePoint 2010 and Office 2010 – it’s always the legacy stuff that will get you.