I would say that 192k would be the minimum quality for ipod use for me. Most of my stuff on the mp3 player is encoded at 320k, and at that rate I can't hear a difference unless I use the main system, and even then it's probably the quality between my CD player and Sansa View that makes the difference noticable.

I've actually never heard anything ripped at 64k. What software are you using? Are you sure your ripping at 64k?