mrqwest mentioned this, so I went to have a look.
It is just like 5x50, but not as prescriptive, and doesn't collect data for you - basically, you pledge to try and run every day in June, and keep a blog (eg wordpress) - but you can do other things if you prefer. There's a facebook page too.
From the site:
''RUN EVERY DAY
BLOG EVERY DAY
LOG EVERY DAY
Juneathon is an annual festival of activity and excuses. Are you hardcore enough to run and blog every day?''
So, maybe a bit crazy (I quite like the mention of excuses!), but as I'm probably going to keep exercising anyway... Though maybe it doesn't add much more than blogging on here. But I'd been thinking about setting up a running blog anyway.
I haven't quite decided yet, but thought others might be interested. So there you go.