I use Bridge for my stash and Lightroom for photos.
In Bridge I tag previews only, not individual papers and elements. I tag designer, store, kind of product (e.g. alpha, kit, 2-photo template, etc.), and theme if applicable (Christmas, family, Autumn, food, etc.) I have tags for all the BYOCs so I can find coordinating stuff easily. As previously mentioned, most designers do a decent job of putting things like "button" or "stitch" in the file name so that's good enough for me and no need to tag more than previews. I also label things when I use them so I can easily find the stuff I haven't used yet when I'm in the mood for new things.
In Lightroom, the photos are organized by date and I tag them with "to be scrapped" on import. When I scrap something, or decide it's not going to be scrapped, I just remove the tag. I use reject/pick a lot to choose the best pics from a series. I used to tag people and places but I found I hardly ever used these tags. I mostly just want to know if it's been scrapped already or not.
When I was on a Mac, I used Finder, and I want to mention something you can do in Finder that I think a lot of people don't know about. You can combine different search terms and then save those searches, similar to a collection in Bridge, but cooler because there is no limit to the number of terms or the ways you can combine them. e.g. you have save a search called "The LilyPad" that searches:
"Allison Pennington" OR "Amy Martin" OR "Amy Wolff"...
Remember the quotation marks!

You can also use parentheses for more complicated searches
(APennington OR "Allison Pennington") AND (button OR brad)
You can do some similar searches in Windows Explorer, but there is a character limit that makes it almost worthless.
