I upgraded my Cybook. PDF support is pretty good, now: no crashes, ability to read even complex A4 documents...
I tried it with a 92-page A4 magazine with illustrations and it worked fine. If I combined the zoom with landscape display, it was nearly comfortable reading!
Browsing is a little slower than with Mobi or html files, though, you have to get used to it. And with landscape, you must use the up-down buttons to read a (printed) page from beginning to end, and left-right buttons to go from one page to the next.
There's still a few things to fix, mostly the management of fonts in PDF documents: with some fonts, especially at large font sizes, the letters get crunched up and untidy. But it's a minor problem, IMO.