Differences with latest stable series (0.8.7) are quite interesting, you can see them all at the Poppler 0.9 Releases list of http://poppler.freedesktop.org/releases.html.
As a summary it includes:
* JPEG2000 decoder based on OpenJPEG
* Some crash fixes
* Better support of malformed files
* Some rendering improvements
So you should be all using Poppler 0.10 now to get a better PDF experience ;-)