I just received notification of the new Adobe X. I was hoping that the one issue that I had with Adobe 9 Pro had been addressed, which regarded the SDI vs. MDI interface. From the discussions that I have found, it appears that the MDI interface has not been re-enabled (even as an option).
I am currently running Adobe 8 Pro and one of the features that is most used is the 'side-by-side' comparison of documents <CRTL-SHFT-L>. And, I do not have multiple monitors where I can drag one image onto another screen.
My IT department installed Adobe 9 Pro on my computer as one of their standard updates. I had it installed on my computer for about an hour. When I attempted the side-by-side function, it opened both documents, each with their own set of toolbars and a separate taskbar, which now made the document I was attempting to view too small to be reviewed. After discovering that the MDI was no longer an option, I requested to have Adobe 8 Pro reinstalled.
Since the introduction of Adobe 9 there have been numerous complaints and/or comments regarding the removal of the MDI feature. There were so many comments posted that Adobe closed the discussion board on the subject. It now appears that Adobe ignored all of those users.