In simplest terms, each user owns Steemit. As an owner, you can see the transactions that affect the blockchain.

As for privacy, I can see what anyone pays into their Steem Wallet and pays out of it, and to who. I cannot see what you paid for (unless you put it in a memo) and if you transfer it to an exchange (ex blocktrades) I cannot see what you bought on the exchange or what happens to it from there (unless I really want to follow the transaction trail on whatever blockchain you bought currency on).

This is really not uncommon with cryptos in general. I can see any transaction associated with a bitcoin address with little work.