Most medium and large organizations using Microsoft’s Office 365 service will also be using “DirSync” to provision and manage user identities. Until now, DirSync has been based on ILM 2007 FP1, which is a functional, but older application, with no x64 support. This means when installing DirSync onto a server, you had to go out of your way to deploy the Windows Server 2008 operating system since the Server 2008 R2 OS is x64 only.
ILM was replaced by Forefront Identity Manager (FIM) 2010, which uses the x64 CPU architecture and as therefore Windows Server 2008 R2 as well.
Today (finally), Microsoft announced DirSync can now be downloaded for use with the 64-bit architecture. This is great news for new Office 365 customers – no more legacy software needed. However, this does raise a question for existing DirSync users: How do we migrate?
You should check out the announcement for details, but essentially, you reformat and rebuild. Wait! Before you start muttering nasty things about Microsoft – the new installation of DirSync will find all of the identities currently in Office 365 and match them up with the appropriate Active Directory accounts in your environment. There is no downtime for the users.
Mike Crowley's Whiteboard 
This is great news as I’m sure the lack of x64 support put some companys off using the tool. You should also note this is by no means a fire and forget tool as there are something’s you should be careful with!! We didn’t have the inhouse knowledge to do it ourselfs lucky enough, our service provider CTX Solutions completed the project for free as part of their new drive for office 365. I believe there no offering it to all news customers also!! Check them out http://www.ictinabox.co.uk/office365.html