Russ Houberg told me about this a couple weeks ago and finally got a chance to check it out.  It's a virtual desktop application running in a browser that allows you to store 5 GB of data and can automatically sync to folders from your desktop.  This will allow you to have you documents on your PC, and soon Macs and Smart Devices to allow your documents to be available anywhere you may have access to a browser.

You can also place security on folders and allow them to be shared with other members.  I know you've seen this from Microsoft before and it's called Office Live or whatever, but what makes this different is the fact that you get a desktop like experience right inside the browser along with ability to sync.  It's also different than products such as Google Docs because it supports any file type, however it doesn't have the office applications built in.

Anyway, you can sign up for a Technical Preview at http://www.mesh.com.  It took me about a week to get My Mesh.  You can also read about Meshes, MOEs and Members at http://blogs.msdn.com/livemesh.

-Chris