Windows Live SkyDrive (formerly known as Folders) is now in beta, enabling end users to store arbitrary data on the web under password access control.  Files can be accessed over http(s) from web pages and from stand-alone client applications (thanks to the http file handler add-on in XPSP2).  Files can be private to your Windows LiveID only, shared with other specific users (via their Windows LiveID), or publicly accessible to everyone on the Internet, anonymously.

The layout feels similar to SharePoint, with web-based directory trees and file metadata browsing and editing.  There's no mention of drive letter mapping (ala file shares) in the SkyDrive intro docs, but I'm sure someone will create a utility to map your private SkyDrive folder to a local drive letter.  It'd certainly be a slick way to shortcut the traditional file upload process.

SkyDrive isn't a web host - it's not intended to be the place from which you run a web app (html content), but you can store files in SkyDrive that are referenced by your web app running on your own server or hosted provider. Browser cross-domain barriers stilly apply: you can easily reference JavaScript or image files stored on your SkyDrive from your web site, but the JavaScript in your web pages will not be able to read or write the SkyDrive files directly because they reside in a different domain than your web app.

You can link to individual files in your SkyDrive storage using plain old URLs, like this: Paradoxes in Web App Development or you can embed a "badge" for the file in your web page in a couple of different styles, like this:

 

or this:

 

You can also embed a folder to direct viewers to whole directories of related file content: 

This will make it a lot easier to post presentation slide decks, podcasts, code samples and demo app source code for blog articles!