No they're not that good, if the arrests are correct then they're actually pretty bad. For the little value that they are worth, they're worth far more as an example to be made for others.
Actually, arresting them is next to worthless. Does the oodles of cash spent each year pursuing, prosecuting, jailing, fining, policing and enforcing vandalism cases result in decreased vandalism? Boredom is a social problem, no amount of enforcement will reduce bored kids desire to break stuff. If anything, drawing attention to Anonymous only attracts more people to it.