You Can. Here is a real life use case:

The users "mralbi" has had 600 BTC stolen by a Trojan on his/her PC (https://bitcointalk.org/index.php?topic=126024.0). The address the funds were sent to is http://blockchain.info/address/1Q3KFL7Z1BTpUboDaU6Qj3t9xCXWpzNntS. On the Taint analysis you can see there are two addresses tagged: "nyana" and Mt.Gox" http://blockchain.info/taint/1Q3KFL7Z1BTpUboDaU6Qj3t9xCXWpzNntS. Theoretically the owners of these tags could be contacted and offered a bounty to provide any information they can on the address 1Q3KFL7Z1BTpUboDaU6Qj3t9xCXWpzNntS. Perhaps they have sent a transaction to that address before. This is just the beginnings of what might be possible in future but does stress the importance of keeping addresses isolated from one another if anonymity is desired.