Best fit, question.

Why when I create polygon with create poligon stream line tool and chnage to object mode (5) Nvil do not Best fit it? Instead it best fit to centr of world axes.

Looks like I understood...Center of poligon is in the world center. Why when create polygon this way it draw not on X-Y plane? Drawing in front view.

I just played around with it and I agree, it's definately not easily predictable where the polygon will be created, because somehow it's dependend on the view.
If you "Best Fit" something in the scene, that's the plane in which the polygon will be created. But if you zoom in, that plane will get pushed towards you and if you zoom out it'll get further away from you.
Your best bet at the moment to create within the XY-plane is to either use grid snapping or reset the view, I guess.

....it's definately not easily predictable where the polygon will be created, because somehow it's dependend on the view.

The "Create Polygon", will draw the polygon based on view angle at a distance of "View Focusing Point".

But why is it that in perspective view the zooming in & out has no effect (which is preffered I suppose), but in orthographic views the zooming shifts the focusing point?

[Edit: Using 'Auxiliary Zoom View' while creating the polygon has no effect on the distance by the way.]

........but in orthographic views the zooming shifts the focusing point?.

That appears to be due to the change made in the sep-20-2013 update, when the ortho cameras where changed to "fixed on zooming".

I would think the change (in focusing when zooming) was not intentional, and probably classed as a bug.

...........but in orthographic views the zooming shifts the focusing point?

You can now change that behavior(update Feb-21) by disabling:- * View > Advance Focus Point On Orthographic View Zooming.