I am working on a script to convert all posts in a given category to use a postmeta flag instead (testing of MySQL has shown me that on a site as large as mine this will lead to a meaningful decrease in query time).
When converting posts I want to just fetch all posts in the category, add the postmeta then remove the category, which will let me just reload that function until there are no more posts in the category.
I can't find a good function for removing a term from a post though. I want to give it the post id and the term taxonomy+ID and have it handled for me.
I am also interested in plugins that can do the conversion for me if anyone knows of one. I couldn't find any that did cat->postmeta, unlike the opposite which can be handled by Scribu's plugin.