Hmm. I still think the term progressive is kinda pretentious. Especially the "music for musicians" part. Musicians all like different musical elements. In fact I think that kind of categorization trivializes the music of those bands, as if somehow the songs weren't meant to appeal to "regular Joes". To say that Rush, Queensryche, Genesis didn't write music in the hopes that musicians AND non-musicians would enjoy it is rather absurd. They were just writing it and performing it with their own style, which just didn't happen to sound like anything else at the time. And I know the early material of these bands was rather experimental and not very "accessible" but that doesn't mean they were writing with musicians as the target audience.

Genexia's rather cynical definition is maybe getting somewhere, though. Sometimes I think in an effort to "keep it real" some of these progressive acts become formulaic in their approach, focusing on adding quirky structural elements to the music and not the sound of the music itself.

I think your explanation that these terms are very time-specific (Progressive = 70's, Alternative = 90's, etc.) is helping me understand the definition better. But that makes me wonder how newer artists could possibly be called progressive when several other of these evolutionary phases of music have already come to pass.

By the way I think the CDNow genres (which are actually all borrowed from the All Music Guide) are pretty silly in many instances... Breaking things down so finely that a single band usually fits into at least ten genres. Not very helpful in categorizing one's music!