I still have yet to see an analysis that picks a random address from the blockchain and successfully identifies its owner by name.
It could be very hard. But if u get an address to be known to belong to a particular service/person, u could evaluate (with some probability) turnover of its capital. Statistical analysis gives quite precise numbers...
Real cash doesn't have such drawback.
Two issues.
1) People don't use one address for everything they do. Businesses, especially, will often create one new address for every customer or transaction. In order to calculate the the "turnover of capital", you'd need to know every address they own.
2) The best methods I know for taking one address and figuring out which other addresses are owned by the same person are checking for multiple inputs and checking for the output that looks more like the change output. Addresses with a lot of transactions back and forth between them would also be likely, though not certain, to be connected. It's extremely easy to avoid all of these with proper control of your addresses. Avoid multiple inputs by intelligently selecting outputs, and by making a series of combining transactions. Avoid obvious change outputs by looking over the input values, fees, and the real cost of the transaction and selecting proper numbers. Avoid having addresses interconnected with transactions by using a lot of addresses; one per customer or something. If you're careful, it's easy to be very anonymous with bitcoins.