I have committed the patch by Ulf Erikson that adds native PDF export (based on PS export code). It has many limitations but at least it's better than what we have now, because it does not require Ghostscript and, most importantly, handles transparency. Complex illustrations, such as this one:
http://www.inkscape.org/screenshots/gallery/inkscape-0.41-CVS-linux-davinci....
are shown quite faithfully by Adobe Acrobat after saving as PDF (though much slower than in Inkscape... and I thought our renderer is the slowest, heh).
Current limitations include: no text (check "Convert text to path"), no gradient on stroke, no clipping/masking/patterns, no eccentric elliptic gradients, no bitmaps.
I know we're probably going to have at least one SoC student working on PDF export, and I think it will make a perfect sense for that student to work on this existing code to improve it. However, even if the student will choose some other approach (e.g. using Cairo), it will be easy to replace this code. For now, however, it's the best we have, and I want this to be in 0.44.