In addition to the performance enhancements and numerous bug fixes, Google has also added several serious feature updates and upgrades. The zoom features should now be working in all ebooks, both pinch and double-tap; it appears to only be good for enlarging images, not the text.
The "Read aloud" feature is now working in most ebooks, though performance is still dependent on the version of Android which you are running. My older original Galaxy Tab has a terrible voice, but then again it is only running Android 2.3 Gingerbread.
The update notes also promise that all text editing features are available for notes, and on my Galaxy Tab that includes highlights in 4 colors, typed notes, and bookmarks.