On the 64-bit platform, these work great together.  The new UI is great and (at least for me) the sync’ing was much better than under the old platform and software.  However, there is a major gotcha that you should watch out for.  If you install and sync under the old versions (ActiveSync & Mobile 5.x) then upgrade, be aware that if it asks you to add a new partnership for the device, “just say no”.  Otherwise, WMC (Windows Mobile Center) will not recognize your device.  Uninstalling everything and re-installing will not resolve the issue.  If I find a workaround, I’ll share it with the group but so far all efforts have not had any effect.