I work with people who use ArcGIS Desktop and they have found the best resolution output images are made by creating PDFs. They tell me that *.png and the rest out of ArcGIS Desktop are not satisfactory and that they do not bother with them. Typically we are making the output appear in a report and so the PDFs of the maps and words are assembled in a PDF editor package to make the final document.
As a result I have been toying around with QGIS on my Windows 7 machine and notice that the best output comes by printing directly out of the map composer.
This output on my Docuprint C2120 printer is as good as any of the ArcGIS Desktop PDFs and is truly impressive. QGIS makes very attractive maps in this configuration.
However, I do not seem to be able to create PDFs or .pngs and then print them which are anywhere near as good. I find the .svg output to Inkscape unrealiable where, for instance, the grid/graticule may come out oversized.
By way of example, the good quality output is where a sub-6 pt font can be read easily off the printed page.
I am using QGIS trunk.