I posted the suggestion for this a while ago, but now I actually have the money to participate in it myself if I actually do it.
The basic idea behind it is that everyone who buys yarn has at some point bought mystery yarn. Unknown fibre content. Some crazy kind of texture that you can't make heads or tails of. But theoretically, it's in your stash somewhere, sitting there, and it's never going to be made into anything.
So I propose a trade. One ball of mystery yarn for another. The fun part of this swap is that you really have no idea if what you're going to get will be useful. But there's always the chance that it'll be just what you're looking for. And even if it isn't, it's always fun to get stuff in the mail.
If I do this swap, I am, however, in need of some advice. Not everyone has multiple balls of yarn in their stash, so it wouldn't be fair to have one person only send one balls, and others to send, for example, 10. Do you propose a limit on the balls? Would anyone be willing to volunteer to send to multiple people, if they have multiple balls of mystery yarn to swap? Who's with me on this one?
(This'll be the first swap I'll have organized, so if I do it, you may have to bear with me a little. :p)