Something occurred to me today about tagging – it’s search in reverse.

When you search, you put in keywords (tags) to find a web page.
When you tag, you take a web page you’ve already found, and save some tags (keywords) for it.

This immediately justifies the value of something like del.icio.us – millions of pages that humans have meticulously tagged with the exact keywords people want to use when people want to find them. That’s an awesome resource when you’re trying to build a better search engine.

However, I still think that tagging is stupid for anything that’s text-based. We already have the technology to derive keywords (tags) from textual web pages.

For photos and videos and things you don’t natively have ways to search with words, tagging makes sense – at least for lazy people who don’t like to write full captions.