Kae Verens has come up with a tutorial using a feature of HTML5 - multiple file uploads.

As a response to a reported bug where Chrome was taking ages to load up a flash multiple-file uploader, I’ve updated KFM to use HTML5’s multiple-file input box where possible.

The code examples in the post show how to use a square bracket ("[]") set in the name of a file upload field, how they're handled on the PHP side and how they can be accessed in the FILES superglobal.