I hadn't ever heard of it before Xenon's post but ran across it again yesterday, reading about some guy managing to cram it into a 171 byte Linux executable. The following is possibly even more of a brainf**k than the actual language and a very good read for those who think size matters (I'm more of a speed guy myself):
http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html
http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html