I'm not good with explanations, so I'm just going to take it from their website:
thesixtyone makes music culture more democratic: artists upload their work for review, but, rather than allow a stuffy suit in a boardroom to decide what's good, thousands of listeners do. The best music automagically bubbles up on our homepage where you can listen to the most popular songs for any genre. It's a quick way to find new music for your iPod powered by pure excitement as opposed to some contrived marketing budget.
Think you've got a good ear? Aside from customizing your experience, creating an account allows you to earn reputation, level up your influence, and collect badges for discovering and recommending good music that others may enjoy. On thesixtyone, tastemaking becomes fun, competitive, and trackable.
We're on a quest to help people fall in love with something new while giving deserving artists an efficient channel for finding their audiences.
I really like stuff like this and the longer I'm on there, the more decent music I find. And I'm notoriously picky. I'm chevalier if you guys feel like adding me should you make an account.
eta: Actually, if you want to sign up, just give me your email so I can send you an invitation, thereby completing one of the quests. THIS IS NOT THE ONLY REASON I WANT PEOPLE TO JOIN, but can be fortunate byproduct. So. Yep.