Ranjan Ghosh on resolution:

The resolution dialog needs a bit of fine-tuning IMO.

1) It's not only the print size that changes but the size on any media. 
Therefore I propose adding a single option"physical size" to
the zoom menu (like 100%,200%, Fit in Window, Physical Size) and
changing the text a bit:

<snip>

Physical Size
----------------
Width:  [---------] (cm, mm,...)
Height: [---------] (cm, mm,...)

The physical size of an image is determined by the
size in pixels, the image resolution shown above
and the physical resolution of the target media
(screen, printer, etc). Most images do not...

<snip>

Now you can enter some value here and when you later select
"Zoom to physical size" you will size the image on your screen
just like it is on your printer. Requirements for this to work:
A proper screen resolution setting in Properties (I would not
repeat it here though as it is confusing) and proper printer
resolution setting. Can this determined automatically? Otherwise
there is a need to enter a printer resolution to (perhaps
in the print dialogue itself or under properties)

The metric system is not needed IMO. The resolution is never
given in dots per centimeter but always in dots per inch. Nobody
- even in Europe - will need that. It's just not used. Even more:
Most people certainly will want to enter some values in centimeter
but read the resolution in dpi. So I propose setting all resolution
values to dpi.