Jimmy Gianninas of Optimal Payments has been kind enough to write a quick example of one way to get file upload into your Flex app. Rather than write a full-blown devnet article which will take weeks to get edited and posted, we’re putting it up on my blog to get it out faster. You can get the examples here. There is a Word document describing some of the files, and then a number of files that you can use as templates to get yourself going. Note that none of it will run out of the box, you must edit files and set up your server as appropriate.
Thanks again to Jimmy for the community contribution. If you have questions you might be better off posting on flexcoders rather than in the comments since I’m not sure how often he’ll check them.