I had troubles getting the nice "Pierre's WordSpew' plugin to work: it did not show any of the posted messages.
I found out what was causing the problem after I checked the error log of my WordPress file:
PHP Fatal error: Call to undefined function mb_substr() in public_html/wp-content/plugins/pierres-wordspew/wordspew.php on line 343
Installing the php-mbstring package (via Yum or any package installation manager that is applicable for your servers system) will easily fix this problem!
(Restart your webservers after installing the php-mbstring package).