I've just joined PMOG, The Passively Multiplayer Online Game and so far, so good. I love the concept - there's no virtual world or universe, but instead you play the entire internet. As you roam the web you encounter mines and loot left by other players, and deposit your own wherever you fancy. You can also follow quests, though I've yet to do that.
PMOG is a refreshing new MOG in what's becoming a crowded market, so it will be interesting to see how it develops. It's certainly got me quite excited. So, come and join me (I'm ione) - you can by my first friends!