I just released a v0.4 of the Remotipart gem, which extends the Rails 3 jQuery-UJS (using the api I built into jquery-ujs a few months back), enabling remote forms with ajax file-upload capability. Here’s the announcement.

Similar to the jquery-rails gem, it now adds itself to the javascript :defaults for Rails 3.0 apps, and to the built-in asset pipeline for Rails 3.1 apps. Installation is super-easy, and the gem basically just works.