I've had a small new idea for a more productive workflow. Most of my work can be conveniently batched into projects. Every project tends to generate a few documents and versions of documents. Whenever faced with a new project, I make a new folder, which becomes a receptacle for files that are downloaded from email. This folder is also located under dropbox, so that the files are available on each computer that I work at. After a project is over, the folder can be moved out of dropbox and back into the appropriate place in my file archive.
It is also possible to place within the project folder other files with information about the project, and to label emails with parallel project name in my email system. Files that need to be shared while working on them can be placed in a Dropbox public folder.
One of the ways in which this system is preferable to the one I was using in that I would download files from email either into a holder directory or to my desktop, and work on documents in various places - sometimes from a folder on the desktop, sometimes in Google Docs.