This is something I've been secretly hoping for for quite a while. I mostly lurk around here, only occasionally having something to say, and that's because I like Arc but I don't use it. I make small experimental hacks, and I like pursuing language design toward a minimalistic, timeless goal which is as open to the programmer as possible... but I hack in Groovy, and the language concepts I think about are not well-suited to Arc (albeit even less well-suited to Groovy ^_^ ).
I haven't started any threads here yet. Until I have something immediate to contribute to Arc, I don't feel like I should, since I'd be distracting from the topic of Arc itself, a topic that's obscure enough as it is. If there were another place with a topic of "Experiments in Programming Languages" or something to that effect, I'd feel a lot more at home.
There's Lambda the Ultimate (lambda-the-ultimate.org). That's not so much for experiments in programming as it is for PL theory discussion - fairly heavy on the academics, but very good.
Oh yeah, Lambda the Ultimate. I've read a few threads there, and I should probably check it out more often, since I can learn a lot very quickly that way.
But yeah, it's not a place programmers come to talk about random general-purpose snippets of code they've made, the way this is. I'm sure there are lots of sites like that too, but I guess I like the balance between that and PL design which this community seems to pursue. ^^