I found Joel Spolsky's opinions to be all over the spectrum. Sometimes he posts well-researched pieces with intriguing conclusions. Sometimes he writes uninformed rants, which show his lack of understanding of the subject matter.
This is not a problem if you carefully apply your own measure to whatever he writes.
I'd say that his ideas on management are interesting and informed. But when he starts talking development or technology he quickly becomes uninformed and poorly researched.
The discussion they had a number of episodes ago regarding MVC "patterns" made it clear that they had no fucking clue what they were talking about. And when Wikipedia didn't give a fast answer they began guestimating instead.
This is not a problem if you carefully apply your own measure to whatever he writes.