We're now on Drupal 4.6 on the Development Seed Blog, as I mentioned in a previous post.  I'd just like to point out a few key features I am really enjoying and look forward to using more. 

The ability to do folksonomy social or free tagging using the Taxonomy module was committed to the head version of Drupal in about mid April, right after the release of Drupal 4.6 and about a month after the Drupal 4.6 code freeze.  This capability was then backported by NAME to work with Drupal 4.6.  We are trying out free tagging on this blog.

Free tagging uses the taxonomy system to hold the terms and then make the corresponding RSS feeds for each term.  You are able to view a list of all terms on an overview screen.  The terms corresponding RSS feed is available just as with any other term.  

To enable the free tagging ability, you just need to create a vocabulary with the taxonomy module and click off to allow for free tagging.  You can assign this vocabulary to any node type, such as blog entries.  Other terms below a vocabulary assigned to use free tagging are able to be created, this allowing a fixed term and a free (user created) term to be assigned to a node.  Then, if a user has the proper permissions to create a blog entry, while entering the blog entry the user will be presented a field to enter the terms they deem appropriate for their post, and can enter multiple terms separated by commas.  

Eric and I had a discussion a few days ago about an implementation for AJAX to allow for the text field for free tagging to autofill as the user enters a letter.  It would have to be done such that as a comma is inserted after a word in the text field, the application knows to start over and autofill based on the first letter entered after the comma and the space - otherwise entering more than one term would be difficult to couple w/ an AJAX powered autofill functionality.  The auotfill would help users tag alike or tag differently based on how folks previous to themselves tagged posts.