The main thing I'm looking at right now (circa October 2010) is PDF 
rendering on Linux, which primarily means the poppler library.  Epdfview 
and Evince are document viewers which use poppler and gtk+ as a backend, 
Okular is a document viewer which uses poppler and Qt as a backend.<P>

I have had trouble with viewing some PDFs, and there have been a lot of 
poppler-related bug on Ubuntu's bug tracker, so this is what interested 
me.<P>

One problem I have had is displaying my <a 
href=http://www.mta.info/nyct/maps/busqns.pdf>local bus map</a> with 
Evince (using the poppler library) on Ubuntu 10.10.  It takes 16 seconds 
for the map to come up.  Eight seconds of that is poppler rendering, the 
other eight are evince.  I wrote a blog <a 
href=http://www.vartmp.com/blog/2010/10/22>post</a> about this.  A 
commit from November 2009 to allow better text selection from tables, by 
doing a topological sort of the PDF, is what is doing this.  Ideally, we 
would have that fix for selection in place, but also speed up display 
for PDFs such as this map.
<P>

Evince is <a 
href=https://bugs.launchpad.net/ubuntu/+source/evince/+bug/665747>breaking</a> 
on Ubuntu 11.04 alpha on gobject introspection suff.  But it is very 
alpha right now so.... <P> 

Evince or poppler is not printing <a 
href=https://bugs.launchpad.net/ubuntu/+source/evince/+bug/664061>filled 
in forms</a> correctly. <P>

As cairo has <a href=http://cairographics.org/summerofcode/ideas>not</a> 
implemented stroke_to_path() yet, <a 
href=https://bugs.launchpad.net/ubuntu/+source/poppler/+bug/664326>some</a> 
PDFs will not display.  Poppler has been following this since at least 
August of 2009.<P>