What is Krumo, and why should I care?
Krumo is part of the Drupal Devel module.  If you want to print out debugging statements in Drupal, you can put this line in your code:

dsm($myvariable);


It will print out the variable info with much more nicely-formatted HTML than just print_r() or similar.

In CiviCRM, I don't use this - I prefer 

require_once 'CRM/Core/Error.php';

CRM_Core_Error::debug('variablename', $variablename).

There are variations on that available here: http://wiki.civicrm.org/confluence/pages/viewpage.action?pageId=33129619

Though this page seems to suggest that maybe the variations are deprecated.