Average users don't care about zoom level numbers, but some people do. Developers do.
I created a 'semihidden' zoom level display for my pages. Google provides hints like "zoom in" and "zoom out" if you hover the zoom control element (slider). I thought that average map users already know those things.
Try hovering zoom slider of the first quadtree example page. Yes, hovering the zoom slider will display also meters/px resolution. That is an extra bonus for those who are interested in the World.
Have a look in the source code. It is commented there as "zoom tooltip hack". Feel free to copy the hack, if you like it. You can molest the code any way you like. Shall this post be the license.