My rejection was simply:

Hello Jeremy,

Thank you for your interest in Google AdSense. Unfortunately, after
reviewing your application, we’re unable to accept you into Google AdSense
at this time.

We did not approve your application for the reasons listed below.

Issues:

- Unacceptable site content

Looking around their restrictions, I really could not find a solution, as I couldn’t find any rule that I explicitly violated.  I posted a request for insight on the forums, and a very insightful user (wasaweb) pointed out my extensive duplicate content on http://jeremytharp.com/ and http://www.coffeecuphalfmoons.com/.  And it’s true — I use my blog’s rss to feed much of the content on my music site.

Since I want to keep the sites separate, I saw no reasonable solution, but then I discovered that recently Google began allowing cross-domain canonical URLs.  Eureka!  I simply set the canonical URLs on the pages on jeremytharp.com that fed from coffeecuphalfmoons.com to the appropriate page that fed the same content on coffeecuphalfmoons.com.  When I resubmitted the AdSense application, it was approved!

Keep in mind that there are a LOT of reasons you might get rejected from AdSense, but given that this was very simply successful, I thought I would share.

I also noticed an immediate reorganization of my site:jeremytharp.com results on Google (for the better).  I’m hoping it has some positive effects on PR on both pages as well.