Image by ThaRainbow. via Flickr
I'm amazed that Google Docs doesn't have a tagging system similar to the one you can use in Gmail, but given this limitation, I created my own tagging system.
I precede each document with a code that makes it simpler to find from the search box. For example I precede each FierceContentManagement post with the code 'FCM'.
When I conduct a search, I enter FCM and Google displays all docs that begin with that code in chronological order.
It's a simple system for overcoming a big limitation. Let's hope Google actually adds tagging at some point, but until it does, this should help.