I have mine in folders by store - though I've gotten away from even picking up freebies from anywhere but GDS because this is where I hang out and participate in challenges and I never end up using the kits I get from other sites.
I have all of my digi stuff, photos, and scrapbooked pages on my EHD. In my GDS folder, I have each kits folder named "kitname - designername" anything that isn't a kit (alpha, single element or pack, template, qp) gets what it is before "template - templatename - designername". I also rename each kits preview to "folder.jpg" which automatically makes it the thumbnail.
I have toyed with the idea of seperating designers into their own folders, but I like being able to see everything at a glance. When a kit has been retired or a designer leave, I move those kits to a seperate folder and when the folder is full enough I burn it to a dvd.
I also have a seperate folder with creative use items.
I have ACDsee, but haven't taken the time to tag anything - I know that once I do that my scrapbooking time will be much more efficient.