Microsoft has thrown open the doors to their Live Mesh technology preview and anyone in the USA can sign up at www.mesh.com if they have a Windows Live ID. Outside the USA will work too, if you are "willing to change your Windows operating system region and language setting to EN-US."
If you are having trouble keeping track, Live Mesh is Microsoft’s Software+Service data synchronization platform announced in April. Sarah Perez (the first link above) describes what you can do with the current preview:
With Mesh running on your computers, you can simply right-click any folder and choose "Add to Mesh." By doing so, that folder and all the files it contains are synchronized with all of your other computers you’ve added to your personal Mesh. It also syncs those files to the Live Mesh Desktop, which is Mesh’s "cloud" – an online web site you can access from any computer. At the moment, the online storage is limited to 5 GB, but that could change in the future. However, Mesh’s recent update allows you to set folders to sync via peer-to-peer, bypassing Live Desktop. When folders are Mesh-enabled, a small panel appears to the right of the folder in explorer which catalogs any changes to the folder (file adds/moves/deletions) as well as notes and comments left by any of the folder’s members.
Live Mesh also lets you access all your “meshified” computers remotely, so if you have software that is installed only on one PC, you can use Live Mesh to access that computer as interact with it as if you were sitting in front of it.
I would have to observe that Live Mesh is required because Microsoft is inextricably tied to applications running on clients which makes synchronization a necessity to compete with applications running in the cloud, a lesson Microsoft has already acted on with Office Live Workspace. However, since today most folks aren’t using cloud applications anyhow, Live Mesh seems very useful.