I'm not sure they are an all too good idea, at least not in articles meant as user documentation, but I have sometimes pondered these.
Usage
The templates would automatically categorize the articles.
As for mockups how would something like this look:
{{todo|To do|Alternative category |nocat=}}
{{fixme|To fix|Alternative category |nocat=}}
Parameters
All parameters optional.
- To do/To fix
- Comment on what needs to be done.
- Alternative category
- Alternative category to add to the pages with the templates.
- nocat
- If not empty the template will not add a category to a page with the template.
Example
{{todo|To do}}
{{fixme|To fix}}
#TODO To do
#FIXME To fix