[eluser]Chad Fulton[/eluser]
I don't want to confuse matters, but I thought that I would point this out to prevent you from having an irrational fear of using the $_POST array.
There is
no reason to not use the $_POST array directly.
The only time it makes sense to use $this->input->post('key') is if you are planning to use CodeIgniter's XSS (cross site scripting) cleaning, in which case you would to $this->input->post('key', true).
Using $this->input->post('key') does not help you in any way, and causes unnecessary function calls, which increases overhead.