The Glog is just the platform, the end product or the collection area for your PBL, reading and writing assignments. It is no different than asking them to create a poster, or presentation on what they have learned or written.
A Glog is the perfect medium for a book report that you have assigned. You still give them them the requirements, Title, Author, Plot, their review, and you can then also have them add pictures, put in a movie trailer if the book has gone to the big screen or record themselves talking about the book. Because of the ability to add links, you can have them link their pictures and videos to the source, creating their bibliography and references.
Teachers are using Glogster as a platform to remix and create curriculum for their classes, differentiating instruction for large and small groups. Glogs can be embedded in school webpages and wikispaces, making them available to classes for homework, parent night presentations and peer trainings. The uses are truly endless. Any subject, any project, Glogster is a great option.
Glogs, give students, and teachers a fun and engaging way to demonstrate their knowledge and skills. If you've assigned a writing assigment, you give your students parameters, guidelines, expectations or a rubric. Glogster EDU is often one option given to students for an end product, along with say, a book report, a powerpoint or poster. It's funny how many choose Glogster though. :) It is engaging, relevant in student's understanding of technology and just plain fun.