just for your info.. i did this before when i start using Vista.. i found a problem after i move all my user's folders to D: drive.
some application/games still use back the old path (C:\User\username)..
mayb it was hardcoded to the application.. i hate this.. sometimes it make me confused that my file is missing.. (especially those desktop shortcut created after install)
Now.. i plan to use Libraries in Windows 7..
First, I create my own new folder (Music, Picture, Video, etc.) in my D:
Then, i add those folder to my Libraries and set it as default..
Hope it works as i expected..