Hi burnttwinky,
Yes, the hard questions are absolutely in line with the current GMAT content. Most of these have been tested over the last three or four years(some go back to 2005) and the style of these questions is the closest to the real exam, in my opinion. You are right that most of the questions in the Official Guide are easy, this is because most of these have been selected from the GMAT Paper tests(where one had less time per question) and Old ETS administrations(where one could only miss one or two to get perfect score). However, if you look at the following questions from Official Guide GMAT 13th Edition: Problem Solving Question#91, 111, 114, 117, 129, 163; Data Sufficiency Question#80, 83, 92, 99, 109, 131 are all examples of questions written by Pearson Vue and more in line with the current content.
I would recommend everyone to practice with these sets. The style of the GMAT is such that the questions are not overly tedious but require some thought. They are all new and the most important part of GMAT preparation is to practice with questions you have never seen before. Once you have seen the solution to a GMAT question, they all appear easy.
Cheers,
Dabral