Your goal is sync the data (music, documents, photos, etc) scattered across multiple computers or even directly access files stored on computer A from computer B. For instance, if you add some new photos to your home computer, they should also become available in your Macbook pictures folder as well so that you can enjoy the pictures while on the move.
Similarly if you have work from both office and home, the documents on the Office computer should be accessible for editing from the home computer and once edited, it should automatically replace the outdated version sitting on the office desktop.
The Solution - When your files are scattered across computers and you hate transferring data via CDs, FTP, email attachments or USB cables, a neat time-saving solution is FolderShare - a free software utility from Microsoft that can synchronize the contents of folders on different computers over the internet.
To get started, you download the FolderShare software on each of the computers that you want to synchronize and then select the folders that you would like to keep in sync - a good example is the "My Documents" folder.
Update: Folder Share is no longer available but a good alternative is SkyDrive or Dropbox.
FolderShare runs in the background and automatically syncs files across different computers. If a particular machine is offline, the document will be synched the next time you connect it to the web.
Other than sync, FolderShare can also be used to download files in shared folders from any computer remotely via the web browser (similar to PurpleNova or Dekoh).
There are absolutely no limitations expect that the maximum size of individual files should not exceed 2 GB. Windows Live FolderShare is a perfect alternative to online backup services like Mozy or IDrive - the moment you connect your computers to the net, content of one computer are automatically backed on the hard drive of the other computer(s) that may be located in the nearby room, your office or somewhere else.
And though FolderShare is from Microsoft stable, it supports file sharing on both Mac and Windows computers.
Related: Synchronize File Folders with Good Sync