We're getting a lot of damage here too. It's like the arrival of summer has transformed the kids into wrecking machines.
We have a lot of wireless netbooks and have had keyboards with the grommets ripped off, broken screen, swearwords etched into casings, etc.
Our vice principal has spoken to the Year 7's and 8's about it (it bodes well for the future that the youngest kids are doing it) and now any damage at all is resulting in us removing the trolley from the room for the rest of term.
I wish we charged departments for damage. It would soon stop then.
Iv had the same problem in the past i i resolved this by installing IP cameras and a large tv screen in the office. left the tv on so the kids could see that they were being watched and it killed the damage over night.
Our PC damage has virtually reduced to zero now we are nearly 100% @VeryPC (the only damage they can do is to USB's which on the whole they havent resorted to). Instead they have switched their attention to mice and keyboards.
We consider these sorts of things to be classroom management issues and push the emphasis back onto the teaching staff. We will departments where we can for any damage :)