Not long after I noticed this I realized I had to have it. I plan to use it in the car.
The documentation is very sparing:http://garden.seeedstudio.com/index.php?title=Music_Shield
But I did get it working with an ATmega328 based Arduino.
I was pleased to discover that all my iTunes (unprotected) AAC files play fine. And I was saddened to realize that he spare 4GB uSDHC card I have will not work, even when I make a 2GB partition.
Now I have to see if I can get some sort of LCD display working.