This will automatically make tags with the tagthe.net and yahoo yql services when you save or update a post. Has the option for retagging all post.
However, I would suggest an option to skip previously tagged posts...
Perfect would be to have 2 options:
-Skip tagged posts
--skip only tagged with web ninja
Also including some other services to get suggestions from would be great like the simple tags plugin has... (OpenCalais, Alchemy, Zemanta, Tag The Net)