Live Mesh, Microsoft's file sync technology has come to the Mac, but you'll need to be running the latest version of 10.5, and be comfortable using a Windows UI to use it.
When Microsoft announced Live Mesh earlier in the year you, like me, probably thought, "what the hell is thing about?" Actually, describing the concept behind Live Mesh can be a little tricky. Certainly harder than describing what an application like Picasa does, for example.
So what is Live Mesh? Put simply, it's a technology, plus a set of applications that Microsoft has developed that let you keep files in sync across multiple different platforms, computers and devices. Microsoft also chose to acknowledge the Mac as a viable platform, and developed a Live Mesh application for Mac OS X too.
In practice, it means that any computer you install Live Mesh on can access a shared set of files and folders. These files are kept up-to-date, depending on which device last accessed and updated them. Microsoft is giving all Live Mesh users 5GB of space, or up to 20,000 files.
Microsoft has also built a semi-slick website that acts like your desktop (unfortunately complete with a Windows Vista theme) where you can access files too. In my brief testing, the web portal worked well, although the metaphor of using a Windows desktop UI in a browser seems somewhat antiquated. This UI however does allow for different 'views' of the file system, including a 'media' view that lets you view images and videos within the folder, given you've installed Silverlight.
Microsoft has also integrated elements of social networking into Live Mesh -- there's a news feed that's also available with the system. Members can invite other users to share a folder, which they can then access on devices in their Live Mesh network.
Live Mesh is still in Beta, but my experience installing and using it on my Mac has been positive. After some initial trouble signing up (I needed to use Firefox as Safari didn't work) to get a LiveID, downloading and installing the Live Mesh application was easy. Files that I added to synced folders appeared online almost instantaneously, and changes that I made on either my local desktop or via the web flowed through the system without issue.
I use Apple's MobileMe iDisk Sync to move files between both of my Macs and while I'm not planning a switch, Live Mesh might be worth a look for you if you haven't chosen a platform yet. Unlike MobileMe
which costs $119 per year, Live Mesh is free, and joins a number of other products that let users keep information in sync across multiple platforms, including Box.net