User agent code for entire application

[eluser]tonanbarbarian[/eluser]
It does matter to a certain degree where you put it
in a controller or model

Code:

$this->config->set_item('my_item', $value);
...
$this->config->item('my_item');

In a library, or if you must, a view

Code:

$CI =& get_instance();
$CI->config->set_item('my_item', $value);
...
$CI->config->item('my_item');

Just be careful, if you are extending some of the core CI libraries, like Input, Router, Benchmark etc they may be instantiated before the controller is created in which case neither of the 2 methods above will work