Anyone having issues w/Content Manager?
It might help to look at the metadata with Windows Explorer, MediaMonkey, or some other tool to verify that the MP3 files have that data. If not, that might be why all your music is showing up as "Unknown."
I just connected my Vita to my PC and checked the files that I did "fix" and they show up fine on the Vita with the album art and song information.
Also, in MediaMonkey, you want to make sure that it's set to save the song information and album art to the MP3 file's ID tags. It's under Tools, Options, Library, Tags & Playlists.
I would not recommend using the Vita as a mp3 player because of the poor battery life and fact that you can get something like a Sansa/iPod shuffle for $50 or less. That then can be used at the gym or just stashed in your coat instead of having to carry around the 4 core, 5 inch oled screen, beastly PSV whenever you want to hear some tunes.
Having said that, I am still annoyed that when the Content Manager Assistant was installed on my pc, it lumped all of the songs into one album. Life would have been a lot easier if the Vita would have shown up as a removable storage drive. Probably another of Sony's anti-piracy measures...