iPod Shuffle
Ok, so I learned emperically that you can’t expect to copy over files to the iPod Shuffle and expect them to play. You have to use iTunes. Also, iTunes can import WMA files but it will convert it to ACC format. I prefer to maintain one file format and the preferred format is MP3 for me so I found this nifty free program to do WMA->MP3 conversion: dBpowerAMP Music Converter
Here are some helpful posts:
iPod Shuffle file structure
Opensource platform independent GUI for the iPod (Doesn’t support Shuffle yet)