As developers, we are all too familiar with code reviews. Having another pair of eyes take a look at our code can be wonderful; it shows us so many aspects of our code we would not have noticed otherwise. A code review can be informative, and it can be educational. I can confidently attribute most of what I know about good programming practices to code reviews.
The amount of learning a reviewee takes away from a code review depends on how well the review is performed. It thus falls on the reviewer to make their review count by packing the most lessons into the review as possible.