Here is a brief description of what mfps can and can't do.
I also add a list of improvements that I plan to add (when I have
the time).

METAFILES:
Not every VDI-Metafile can be postscripted by mfps. Namely, metafiles
created with Easydraw 1.0 give strange results, because E-Z-draw fails
to update the metafile extents when creating it. This problem is
fixed with Easydraw 2.0.
Metafiles produced with the new version of GEM-Draw (2.0 as far as
I know) cause trouble if they contain 'free-hand-polylines'. This
function is broken in GEM-Draw and causes non-standard Metafiles
to be produced. Mfps reacts ungracefully (bombs) on this kind of data.

SIZING: 
The original scaling of the graphics is slightly altered.  However,
all the proportions are the same on screen and in the printout.  Not
all formats work really good.  Best results are obtained with DIN A 4.
Worst results come with DIN A3. The program was implemented in
germany, so DIN formats are preferred. Unfortunately, I had to
introduce some format dependency to the program, because the LW cannot
mark all of the physical page.  I think the actual marking-correction
values should be read from some kind of environment or a configuration
file. Maybe in a future release. 

FONTS:
The new version of mfps (6.1) has a lot of bugs fixed. Most of those
bugs were related to the way text is treated. The dimensions of
graphic text is now precisely the same as previewed on the screen.
However, there is still a way to get 'ideal' spacing, when text is not
format- or dimension sensitive. With the exception of 'shadow', all
GEM font-effects are now supported. This is important for Easydraw
users. Outlined text will always be printed with the build-in
PostScript spacing -- sorry!  Mfps believes, that Helvetica should be
used as graphics font and therefore takes Helvetica as default
(system) font.  I have only working experience with Helvetica and
Times fonts. It might be critical which font is mounted in which
position, because mfps has it's own idea about that. 

ARROWS:
Mfps draws very nice arrows at the end of polylines. The arrows
are MUCH prettier than arrows drawn by most other programs (namely
MacDraw). However, creating nice arrows was not easy. To support
the arrow line-end style for elliptical arcs was too hard to do
for me. Maybe some knowledgeable soul comes up with a good solution
some time.

PATTERNS:
Most standard fill-patterns are implemented. Not implemented are
fill-styles 2/14, 2/15, 2/22, 2/23, 2/24 of the VDI specification
and user defined patterns.