If I remember correctly, Joel mentioned in one of the podcasts that he likes to just tell stories in his blog posts now and let audiences draw their own conclusions. When he tried to make arguments before he was often misinterpreted (e.g. his stance on exceptions) and now he feels he has to pre-respond to the multitude of ways people might respond to his argument, and that doesn't make for fun reading. As he's gotten older and more experienced he also said the world has become less black-and-white so he doesn't like to make absolute statements as much anymore.

The podcast is linked off from here: http://blog.stackoverflow.com/

He also writes a column in Inc, which isn't bad: http://www.google.com/search?q=joel+spolsky+site%3Ainc.com

I don't think the quality of the posts have gone down all that much, just the quantity. I imagine he's just run out of things to talk about that he hasn't already covered.