I did the first 41 passages in Khan bio/biochem, and I think they are great resources because they are so difficult. If you haven't done any yet, I highly recommend doing them because they are a cut above the mcat and will help you prepare at a higher level than what you will primarily face on test day. The occasional few questions (particularly on psych/soc) are out of the scope of the mcat (Lazarus theory comes to mind, there are a few other random terms that come up that were found nowhere in Kaplan/TPR psych books) but everything else is fair game imo, if not asked a in a more depth level of detail or hidden or more difficult to understand passages.
For me, the Khan passages in bio/biochem and psych/soc was the big wake up call I needed to work harder to understand passages after going through content review. The physics passages on Khan are more straightforward since they aren't pulled from journals (it appears), from what I can remember.
