Like most other ebook readers, ADE is flat text oriented. Zooming applies at the character level (by inflating/deflating font size) with text reflowing. Suppose that the ebook contains large pictures (as large as a page size) or that the epub file has been converted from pdf in the picture mode. In this case, each page of the book is converted as a picture and the inflating/deflating text size functionalities available in ADE does not produce any effect at all.
Converting from pdf to epub in picture mode is absolutely necessary when the page layout must be preserved (the ebook readers should get out from the "text = flat character string" logics that take us back to the stone age).
Depending on how the epub file was generated, two cases can arise in the situations previously described. Either you get something so small in the ADE reading window that the text/picture is unreadable, or you get something so large that the text/picture gets truncated at the bottom of the page. In the first case, ADE turns out to be unusable because there no zoom-in functionality. In the second case, ADE is unusable as well because part of the text/picture is hidden and there is no way to get access to it: no lift and no zoom-out functionalities.
Since ADE is based on Flash, it should be easy to introduce real (not character oriented) zoom-in/out functionalities. For instance, anything that could look like the zoom-in/out mechanisms found in the Mobipocket reader.