I just saw this as the top article on Major Nelson's blog and figured some people might be interested.
http://skydriveteam.spaces.live.com/Need a place to store your stuff ‘in the cloud’ ? Sign up for the Windows Live SkyDrive Beta that was just opened to the public. This will give you 500 MB of storage that you can access anytime, from anywhere you have a PC. It could come in handy if you are on the run or traveling all the time. It has the option to store files available to everyone, just friends or only yourself.
Edit: Yes, it works with the Mac. I took some screen shots of me using SkyDrive on my Mac in both Safari and Firefox and shared them here.
I just signed up and it was pretty painless. You can use your existing Live ID to sign in and get started.