"I found a podcast in the Apple iTunes store called "Using Outlook's inbox to manage tasks."
I can't seem to locate the podcast you refer to. Could you please tell me if it has a different title? I'd really like to listen to it.
For what it's worth: I use the single folder method with categories for filing away my email message. I have a folder called "Processed Mail" and I make sure that each message has a topic/category before I file it there. I'm a software add-in geek so I use Speed Filer and Clear Context on top of MS Outlook 2007. I tried to GTD add-in but didn't really care for it. I just couldn't seem to get the hang of it....
I also convert emails to tasks all day long (since most of my work world is electronic). I categorize my tasks with @calls; @computer; @home, etc. and then make sure my Task List is sorted by Category. It works quite well.
Let me know if you have questions...I'd be happy to help in any way I can.