The idea about leetspeak is that if you use it you're 1337 or 31337 (leet or eleet), that is, "elite". It was created by hackers --hence the numbers instead of letters-- and its only use is boasting. Every time I run into some leetspeak I've got to check a proper dictionary:
<p>http://www.urbandictionary.com/define.php?term=leetspeak
<p>Although by now I've already learnt some of its basic words.