From my experience in July 2011 (Yoyogi, Tokyo):
They look into your bags when you enter the venue (not touching anything, not asking you to take anything out). Also, they ask you if you got a camera with you. If you want to, you can leave your camera at the entrance and pick it up again after the concert has ended.
As the others already said, outside the venue you can take pictures as you please. I saw many people take photos with the goodies or ayu wallpapers.
When you're inside the venue, you should be super careful if you really plan to take your camera or cellphone out. I didn't try at all and just stuck to their policy, even though I think it's too strict and would've liked to have "personal" concert pictures.
But in the end, when you're there and spoil the fun of the concert by being caught and told off by the staff, I don't think that's worth it.
When I was in the Stands (far away from the stage) I didn't see security persons at all, but at the day I had Arena seats (close to the stage) there was a security guy walking by the rows every 5-10 minutes. He really distracted me sometimes, even though I by no means had plans to record something but just enjoyed the concert.
And he even bowed down to check if someone hid a camera at waist height.