...just to add and talking from experience...
...it is a characteristic when outlining typefaces for them to appear thicker when output to a highend device (CTP). This will be much more noticeable when using small thin typefaces in paragraphs for example...
...we often get designers artwork all converted to outlines on some pages and not others, the paragraphs that have not been converted to outline will look thicker when printed through a postscript rip due to the calculations involved in making the shapes...
...best to keep text as a font or convert the whole lot to outline rather than mixing it up in a publication. The difference is noticeable depending on the typeface, size and amount it has been used in a publication. This can lead to a rejected job from clients and therefore a reprint at a loss, so be careful...
andrew