I attended all three courses at ISBA in spring 2006. For me it was definately worth it, and of the other students that I talk too they were happy with the results as well.
James (Owner/Instructor) is very good, patient instructor. Since he wrote the text book he has excellent knowledge of the subject and was able to stuff our heads with a broad understanding of the topics. Your milleage may vary, but I left my computing carreer of 15 years to take on this challange, I felt confident after the course to build my own timber frame projects, and since then I have risen 2 frames with a third on the way.
In particular the content allows the student to build with irregular wood. Common in the industry is perfect wood, kiln dried and planed to square within 1/32nd of an inch. James' method allows the builder to build with green, twisted, or recycled timbers. Allowing buildings to be built with economy in mind.
The school is good and the tools are in decent shape. I paricularily appreciated the numerous Electric Stihl Chainsaws for the log component. The mortising machine, large maffel planner, 21" circular saw, allowed me practise time to use these tools before I had to use them in production. Not to mention all the other tools that come with the job.
In the three months we 2 frames, 1 Log on Log, and a modular log post and beam building, allowing us plenty of experience. There is no computer CAD component to the course which at first I thought might have been good, but now looking back I'm glad there wasn't because it would have taken away from the issue at hand, learning to build with wood.
Of course, take notes, lots of notes, practise hand drawing everything, it helps immensly when training someone and you can wip of an isometric of the joint your trying to cut. Read the Text before you get to the course, cause you'll only want to do review during. Register early and find accomadation through the school, they'll hook you up with decent accomodation.
Lots of fun, highly recommend it.
Billy