The first reports about the The Official Guide for GMAT Review 12th ed are coming in:
The book is said to have about 30% new questions, including some bold CR's. Overall the format remained the same and some of the older questions have been replaced with newer ones - no new concepts have been introduced and the new questions are still testing the old principles/concepts. This seems to be in line with expectations, though definitely kudos to the GMAC for including new questions, though more new gmat questions would be nice. I will have to wait until later in the week for my book to arrive.
Here is the feedback on the Official Guide 12th edition from one of the GMAT Club's members:
It is basically the same as the 11th Edition. About 1/3 of the questions are new, all of which test the same concepts as the ones that have been replaced. If you already have the 11th Edition, there's no need to buy the 12th. There are several boldfaced CR questions, questions that have already been posted in gmatclub. (source: http://gmatclub.com/forum/the-official-guide-for-gmat-12-merged-76806.html)
As a reminder, the Official Guide 12th edition is coming out on March 23 on Amazon - we have written about this book in more detail in this post: http://gmatclub.com/blog/2009/02/the-official-guide-for-gmat-review-12th-edition-is-out-on-march-30th-2009/
Other books in the works by GMAC:
The Official Guide for GMAT Quantitative Review 2nd Edition - expected in September 2009 with 300 total questions, 75 of which are new.