Thanks for the input. It was great! I too have been frustrated with the simplistic filing mechanisms that computers impose on us. This is roughly how it will work...
There will be a "Classic"

mode that works the way it does now, but you will have the option to go a tree-based mode, a la Windows Explorer. You will be able to define a hierarchy of categories, not just the simple one-level system we have now, and you will see them as a tree in the My Channels window.
Channels can be assigned to more than one category and will appear in each category in the tree. You will be able to drag and drop channels around the tree i.e. add/remove them from the various categories. If you delete a channel, you will be asked if you want to delete the channel or just remove it from that category. And so on. Hopefully, this will alleviate the problem of a burgeoning number of feeds and how to manage them.
I'd like to somehow tie this in with the ability to show/hide channels based on filters since I think that's a really nice feature. Once you have several hundred features, showing them all at once isn't practical.
I'll have to mull over it a bit more...
