Via TUAW, a handy little app called Dockdrop. From the website:

Drag any file or folder you want to share onto the Dockdrop dock icon then choose how you want to send it. Dockdrop uploads it and puts a URL for your upload on the clipboard, ready for pasting into an Email, chat program or website.Dockdrop is currently available completely free of charge.

It currently works with FTP, Flikr, WebDAV and SCP—and Apple's dotmac uses WebDAV. That's great, because if I want to upload a file to my idisk quickly, without loading it, navigating to Sites, copying the file, and ejecting it, this is perfect. Unfortunately, Dockdrop doesn't have any instructions, so here's what you'll need to do to get it to work with dotmac and your idisk:

• In the preferences, select the WebDAV pane and make sure that 'Enable WebDAV upload method' is checked.Then set the following fields:
• Server: idisk.mac.com
• Username: your dotmac username
• Password: your dotmac password
• Path: /your dotmac username/Sites/
• Web URL: http://homepage.mac.com/your dotmac username/

The Web URL should be automatically filled in as you enter the Server and Path information, but you'll want to have the homepage.mac.com URL when Dockdrop copies the URL to the clipboard. Also, the Port is automatically set to 80, and that seemed to work fine.

One thing I've already noticed is that the current version of Dockdrop doesn't seem to register whether the file you're uploading is replacing another or not—so there's no dialogue asking if you're sure you want to proceed. You'll have to be careful to give your files a unique name. But other than that, it takes a lot of hassle out of uploading files. Definitely worth a look.