Drag-and-drop attachments, a feature which lets you drag files from your desktop machine right into your e-mail message to have them begin uploading, and hence save you a lot of time .
It works the same as the system Google implemented in its Wave service for photos and other media types. It also has the same requirement of the user having to run Google Chrome or Firefox 3.6.
The drag-and-drop attachments is really the new, killer feature. For those users on Chrome or Firefox (with Mozilla’s Prism installed) who are running Gmail as a standalone desktop Web app, this adds a whole new layer of functionality, and one that more closely resembles a real piece of software.
Google software engineer Adam de Boor wrote in a blog post, "Suppose I want to attach some files to an email, and I already have a folder open containing those files. I used to have to click ‘Attach a file’, find the photos, click them, etc. [Now] I can just drag and drop the files to attach them.
For now, you can drag and drop attachments in Chrome and Firefox only.