Inside the official announcement of some upgrades to Google Documents is this section about the new "folders" feature:

"Almost from the day we launched people have been clamoring for folders. They're here! [...] documents can live in more than one folder at a time."

I don't know about you, but where I come from, that's not a folder; it's a tag. A folder is meant to be a real-world representation of a manila file folder, and I don't know of many real-world documents that can bend the fabric of space to be in two different file folders at once.

In order to avoid watering down the definitions of both tags and folders, Google should call a spade a spade and a tag a tag.