I've got about 1-2 thousand lines of code lying about in tiny programs I've written playing with it, and I did enjoy it. I just never seem to have a size-able problem that's a good fit contemporaneous with the itch to learn it.
So a subleq virtual machine here, a markov chain there, but I've never managed to really sink my teeth in.
In both cases it was a good fit and the language was fairly pleasant to use, if a bit verbose and pedantic to my Ruby-and-Perl-accustomed brain.
It's certainly worth playing with.