Leet speak is often used by otherwise non-lamers for sarcasm and humor. This is because 1337 sp43k 15 1nh3r3n7133 hum0r0u5 (leet speak is inherently humorous). It's also kind of fun to type when bored, as it gives one cheap laughs.
Also, leet speak for porn (pr0n
) has become somewhat mainstream
. It even appears in the Jargon File