I had a bunch of 192kbs MP3's in iTunes and decided to convert them into 128 AAC. I did this fine, but when i plugged in my iPod to sync, i am sure its capacity left was going down. I don't know why. I know i hadn't added any more songs, all it was doing is swapping the MP3's for AAC's, and i had removed the MP3's from the library aswell. Is it that if you delete songs from the iPod it just leaves a gap.