I find that the PDFs work fine, but they're scaled to fit the screen. (one of the reasons I picked up the KoboEReader was for PDFs)
So fonts and glyphs on pdfs that are formatted at 8.5x 11" appear small.
I agree that the zoom scroll is a bit cumbersome, as page jumps occur once you hit the edge of the page. ie. button click at the Right and Bottom of the page will jump to the next page. This Auto-Page jump coupled with the delay that most eReaders have could be frustrating to users who need to zoom and pan pdfs.
If you're creating documents I'd reccommed either PDFs formated for a smaller page size (ie. maybe customized to the device screen) or converting to EPUB (as fonts can be resized dynamically on the reader using EPUB books).
Here are things that i'm hoping are added in the next Firmware:
+ Ability to Jump to specific pages in PDFs
+ An alternative method of zoom and pan