Put your files into your Dropbox folder on one computer, and they'll automatically appear on any of your other computers that also have Dropbox installed (Windows, Mac, and Linux too!). You can even download Dropbox apps for your smartphone or mobile device (iPhone, iPad, Android, and Blackberry). Everything in your Dropbox is available from the Dropbox website, too.
You get 2gb storage for free and it works absolutely transparent in your os of choice so you just use finder,explorer,command line or whatever to manage your files and dropbox does it's magic in the background.
Its also a great online backup and revisioning system.
Oh and did i mentioned it allows you to share files with friends and family?
It's an really awesome app which i use daily for work and private stuff (syncing between work pc,macbook and iMac) and i can greatly recommend it.
In case you wanna try it, please use my referral link it gives you and me 250mb extra space.