How much privacy do you give your preteen? At this stage DD11 has privacy in the bathroom, i.e. you must knock and she will decide if she wants to let you in, but she still regularly invites you in for whatever reason and also walks around the house naked.
Room - she doesn't want us to go into her room without permission, whether she is there or not. I think this is a step too far, it is still a part of our home and at this age we need to know what she is getting up to.
Electronics - we reserve the right to look at what she is doing on her laptop at any time, as well as access email. Her cellphone went through the wash (and died) and she doesn't feel like saving up / working for a new one so that's not going to be a problem any time soon.
We have DS 12. Like you we knock when he is in the bathroom and wait to see if we can go in. We also knock on the door when he is in his bedroom, but he knows we will walk in once we have knocked. If he is any other room in the house then we just walk in, if the door is shut.
My daughter is 12 and I'm only allowed in the bathroom for something essential (like she has forgotten something she wants to take in there) and I'm not allowed to look. If she's in her room and the door is slightly closed, we now always knock and ask if we can come in.
I'm not allowed to see my daughter, but if she has a sleepover with a friend it's okay for them both to see eachother naked!
We don't check her electronics as screens are only used in our living room, ie computer, laptop or ipod so most of the time you can see what she's on.