Same here...
MJ is climbing all over things and doing it all with a cheeky smile on her face, she knows that she is not allowed to do it, but kept doing it.

I lost my cool the other day when i found her on the computer desk playing with the fax - i only went to the toilet and she beetled off to climb while i was peeing this was the third time for the day that she had been up there - each time i had take her off or got her to climb down and explained why she wasnt to climb up there...
Anyway so this last time i found her on there i told her off, more i yelled at her (which i am really not proud of as its not how i wasnt to parent - but lack of sleep and a bit of fear - its quite high up) then i stopped took her down (she was crying at this point) explained that it was dangerous and i told her that she had to go into her room.
I put her in there and closed the door and count to 30 (i think time out is a minute per year but 30secs was enough and i wasnt expecting to use T/O this early on) I went in and cuddled her straight away and talked about it again
She has never been up there again, nor has she done something similar.

Dont know if this is something that you are thinking of doning or would be appropriate. I did feel awful shutting the door, but im not a smacker and i think that she did need to learn a lesson.

I am finding the boundry pushing increasing diffult - especially on days when MJ has a biig molar movement