no advantages to reformatting it, other than you can access it using both windows and mac.
getting the music off the ipod is pretty easy if you enable hidden folders, however you lose the playlists.
oh... and if you're using USB, forget about it! It'll take you years to get stuff off.
I keep my library on both my iBook and my MacBook. I update the iBook like every few weeks with what's on my MacBook.