Just a little tip.
I often wonder what size a window has and/or where to put an element.
Sometimes I see an application window that I like but need to know the dimensions to really mimic it.
It is nice to know, sometimes, where a window is on a screen.
And there is much more one can think of.
A few months ago I came across a nice litte application that helps me to solve all these questions: xScope.
It has a loupe, guides, rulers, crosshair etc.
Very, very useful!!!
You can find it here: http://iconfactory.com/software/xscope