I still do love my 600, but since I bought my ipad a week ago, I haven't used the 600 for technical pdfs anymore. So zooming (besides reflow for novels) is not necessary anymore. I now use the 600 for novels only but must admit that the 300 or my old 505 would do that trick too.
I've bought goodreader for ipad and it's awesome to just set the margins in a pdf on the fly. I'd love to see something like this for the 600, too, as I think I'll use it mostly on the road now. And the ipad just isn't that great for toting around compared to the nice small form factor of the 600
