Publishing usernames was pretty pointless assuming you can already see them on the site. All they did was take down some sites, which I would assume the FBI was already watching making it harder for them to do their jobs.
The FBI has already raided multiple sites on the TOR network, and even caught people. By bringing down the sites they are taking that away from them.
Anonymous don't think before they do, they just act. I know if I was working for the FBI and was watching some site then learned Anonymous was attacking the site, possibly destroying some evidence by crashing the server I would be pissed.
Seriously, they need to leave the "catching" to the pros.