I recommend licensing/grabbing FB Reader as the jetBook does. Its PDF handling is far superior to the Kobo's; I hadn't realized how superior until I started trying to read a technical PDF.
Zoom in/out of about 7 layers which sticks over page turns. Excellent reflow which makes reading an image-free PDF as close to painless as reading an ePub or txt file. Divide the page into sections and page up/down/right/left for each chunk (great if you have a multi-column PDF and/or or lots of graphics.)
Since its GPL I'm assuming Ectaco's source tweaks are available as well (if they tweaked it.)