Speaking as someone who is sick of stuffing a pocket with a palm pilot and game boy every day (and constantly worried about the fragile $300 device) I would love for the DS to have an organizer. I don't need a full set of Palm features, but a contacts list, calendar, and note pad would add a tremendous amount of value to the DS for me.
If Organizer Plus or any similar software launches with the DS, I will probably just stick may palm pilot in a drawer. As for MP3s, I never bought the memory stick my Clie required to play MP3s, as I really only listen to music in the car. The only time I ever listened to music while stationary was while writing long papers, but I have been out of college for some time and I just use winamp if I ever do write anything at home. My job also requires me to use a phone too much to listen to music there.