I'm disliking the navigating too, but instead of the spacebar, I have to hold down the Command button at the same time. The problem with that is it takes me out of Model Space and into Paper Space. Two double clicks to get back in and all is well, but it took a while, and when you're concentrating on eg, dimensioning, you don't always notice.
Re: inactive windows. No zooming, but side to side movement is ok. A fix would be nice.
My other problem bugged me so much I went out and got a (insert feeling of embarassment here) Logitech wheel mouse, and that was trying to control the zoom rate. When it's set as slow as possible, it's too slow for everything else and when it's in AutoCAD, it's ok but most of the time it takes 3 or 4 swipes on the scroll to get it to move. The wheel mouse was ok, but zoom control doesn't work well, even tho it's an expensive mouse, and exchanging it for a new one brought the same problem. (let go of the wheel and it bounces back a little...or a lot... from the direction in which you zoomed). I think I'll take the magic mouse...