One thing to understand is that it's trivially easy to create a new address.  Takes your computer a fraction of a second.  So you can create thousands of addresses, have bitcoins sent to any of them, sent from any of them, and have them sending to each other, internally.  From the outside, nobody knows who controls which address though.

But they can try to guess, and trace things back.  http://blockchain.info/ lets you look around all the transactions.

If you're really paranoid, there are "mixing services" that let you send bitcoins to them, and have bitcoins come to a set of addresses you specify at some later time, from different addresses than where you sent them.

So things could be traced back to individuals, if they use the same address for everything, and post that address publicly.  But in most cases, there's no way to know who owns what.