Tagging is huge!
Interesting Tag statistics from Technorati in their State of the Live Web (April 2007) report:

• 230 million posts per month are tagged, up from just 200K a couple of years ago
• 35% of all posts tracked by Technorati use tags
• blogs a now heavily using tags

I believe that the future search algorithms will more heavily use tags. The combination of content creator assigned (blogs, mainstream media, etc.) and user defined / selected tags (del.icio.us, etc.) will be a great way to search for information.