If you have a Windows PC, you can see how the Sony PRS-600's "reflow" PDF option will likely look using Sony's Windows ebook Reader
. This program now emulates a PRS-700, which is similar to the new PRS-600. Both will probably also have a "zoom" mode, although this isn't apparently very useful for routine reading on the PRS-700. It will also have a landscape mode, that will provide a half-page at a time magnified view of the PDF (as well as reflow, like the portrait mode).
It is commonly assumed that ebook manufactures (with the exception of Amazon) are waiting for plastic screens before introducing their 9.7" devices. These should be available this fall. Note that a device with the PRS-600's firmware but a 8.1" or 9.7" screen would be the "PDF viewing" option you are looking for. Another possibility is Mainstream iRex 8.1-inch reader for 400$ (rumor)