Nice. I installed this but I have it disabled at the moment as I'm not comfortable with plugins (or hacks for that matter) yet.
By the way, you might want to surround the template code with this:
Code:
<if condition="$vbulletin->options['enablehooks']">
<if condition="$user_joindate">
</if>
</if>
It will disable the template code if the plugin system has been disabled or the plugin has been disabled.