There are a lot of discussions online about Fair Use of music, and the US Copyright Office is the place to go. They have a PDF of the complete U.S. Copyright Law and a list of sections so you can find what you need. But basically, this is what I learned from looking at the PDF:
"the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright."So if you're going to use music as a way to make the podcast more interesting, even if it relates to the discussion, then it's not fair use. But if you're going to play a piece of music to critique it, then that's okay. Basically, when in doubt, get a license or permission, even if it's just for a few seconds. I got permission from a band to use their music in my podcast's intros and outros, but I guess I'm going to have to scrap the style of the latest podcast I did because I'm pretty sure it doesn't fall under Fair Use.
So now I'm wondering if all that work was a "waste" of time, but I guess it wasn't, because I was able to do this post. Plus, it was just an enjoyable thing I did, and maybe down the road my production skills will be put to use based on the practice I just had :D