Outlook 2010 x64 will not sync with your mobile device using Windows Mobile Device Center. You must install the 32 bit version of outlook 2010 if you want to synchronize with your mobile phone or PDA.
The worst part is there will never be an update to make WMDC work with the 64 bit version of Outlook 2010.
quote:
The WMDC will not be upgraded to work with 64-bit Outlook 2010 or Outlook Click-to-Run.
-Microsoft
http://office2010.microsoft.com/en-us/sharepoint-designer-help/microsoft-office-2010-faq-readme-HA101793215.aspx#_Toc257626208