On most of the blogs I write for, I usually forget about adding tags. I have always been a category user, not adding all of the tagging plugins that are currently out in the marketplace, and really not taking up tagging, even though it is now in the core of WordPress, but some new plugins by Calais might just rectify that issue for me by helping give tag suggestions automatically.
Found thanks to ReadWriteWeb:
Grossman’s plugins, which are available as an auto tagger and an archive tagger (to go back and tag old posts), received over 500 downloads in the first two days. The plugins work by sending post text to Calais and retrieving a list of suggested tags. The plugins rely on an Open Calais PHP class, also written by Grossman. Eventually, the plugins will be released under a Creative Commons license. Grossman tells us he’s waiting until the next Calais feature update, scheduled for May 1st, before adding any more features to his plugins.
Not only can you install the WP Calais Auto Tagger to help you tag your posts from now on, but they have also developed the WP Calais Archive Tagger which will go back through your posts and tag them based on a semantic examination of your posts.
For those worried about tags they have already added, the Archive Tagger will not overwrite those tags, but instead add to them.
The plugins require PHP 5, and the cURL library which many hosts have, but not all, and so check with your host before installing these plugins.
Read more about them on the WordPress Plugins library under WP Calais Auto Tagger and WP Calais Archive Tagger.