At long last WordPress supports tags. It has always had categories, but you have to set these up beforehand and they are only really useful as broad subject headings. They are usually displayed in a side bar on your WordPress blog, and the list becomes far too long and unusable if you treat categories as index terms or very specific, one-off tags. One of the problems I had when converting my Blogger blog plus tags to a WordPress blog with categories was the huge number of categories the conversion generated. I spent about half a day pruning the category list. Now, as well as assigning categories to a posting, WordPress lets you assign tags on the fly. I am not sure how this will affect the Blogger to WordPress conversion programs, so would be interested to hear from anyone who tries it with the new system in place.