I have Instapaper delivered to my Kindle. Since the Kindle treats it as a periodical, lots of old Instapaper docs piled up in my Archived Items. You can delete this on the Kindle by taking them out of the archive and then deleting them, but it’s so. dog. slow.
Archived Items are cloud synced and can be managed in your Amazon account, but there’s just no way to bulk delete things in the web interface. Somebody solved this with a nice little bookmarklet, though. Somebody Japanese, I guess.
Here’s the bookmarklet in case the original page disappears:
Just press the bookmarklet, type in the keyword (in my case, Instapaper… it appears to be case sensitive, and if nothing matches it just doesn’t offer to delete anything), and then press okay to delete the matching items on the current page