So @GooglePlayMusic has been showing signs of that, oh so worrying, Google product trait where small things start to not work properly.
For sometime now the web interface keeps telling me there's one more song uploading. I have no idea what it is. I click on the icon, taking me to the 'recently uploaded' screen, to find everything there.
When adding the last four free Underworld tracks, Google Play Music has given them all the same artwork, even though they each come with individual covers. These covers can be seen when looking at the file locally, but in here they are all the same. Which brings me on to my thrid thing...
Cannot upload artwork
At some point Google Play Music lost the ability to upload cover art for tracks or albums. I can pick a new piece, but it never uploads. This means missing, or wrong, artwork can't be fixed.
I moved away from using iTunes and an iPod quite some time ago, but that option may need to be dusted off (literally) again.