This article sums up a few of the options in uploading i've seen. It discusses a flash and rails uploader, mongrel uploading, a java applet drag and drop, hidden iframes uploading and multiple file simultanous uploads.
The Beginning of Rails Upload Progress Bars
Not long ago then Rick Olson published an explanation and plugin for mongrel to do progress bar monitoring. That plugin can be found here:
There is also the way google does uploading for gmail with a hidden iframe which is explained in this tutorial.
What still is being worked on though appears to be the issue of uploading multilpe files simultanously and furthermore to watch simultaneous uploads with progress bars or even progress stats. This is an obvious valuable feature for people who do large file uploading in their sites.
Now, there are a few options out there that you might consider.
Flash and Rails
The first one is doing Multiple File Uploading with Flash and Ruby on Rails. This one has a nice to use interface and seems workable if you dont mind using flash in your project.
Java and Rails
This one here Rad Upload opens a java applet that will let someone drag and drop files into the applet and autouploads them with progress bars. Ive yet to see a rails implemention of this though but I would love to. It comes with php and perl examples but no rails.
What else is out there?
My experience being only limited to what ive found through searching, there may already be some solid options and examples out there I don't know about. I hear Ezra is working on multifile uploads all in mongrel but have not seen it yet.
I'd personally really like to see a robust file uploading manager availabale that is open source to the rails community. Perhaps some of the tools shown here in this article can lead to the developmont of a multiple file progress bar based uploader.