Keeping documents up to date between computers has historically been fraught with difficulty. But the folks at Dropbox have made the process drop-dead simple.
Dropbox creates a folder on your hard drive (for as many computers as you wish). Any files that are placed in that folder, on any computer, are uploaded to the server and then synced with every other machine. As long as your computers are connected to the internet, everything is kept up to date automatically. You don’t have to worry about which version is current, as it keeps files updated whenever you save them.
You can also create shareable folders within your Dropbox folder, and give access to anyone you like. This is helpful when needing to send large files, or as a central place for keeping project related materials up to date for all team members.
For advanced users, Dropbox can enable you to do some pretty slick things. You can keep your passwords in sync, print articles and web pages as PDF files to read later, sync your iTunes library across multiple computers, or keep your Things installs synced on multiple machines (which has increased my use of Things considerably).
Dropbox is available to Mac, PC and the iPhone.