There are no precreated folders so no one uses them. If you are talking about osx then yes many people do.
I do not like that there are tons of packages included in ubuntu-desktop that I do not want. I remove them and it doesnt bother me. Look this is something for a new user. If you ever had to deal with someone who is computer stupid you should know that if they arnt given folders from the start everything ends up sitting in a slue of 'New folder 1-1million'.
As for smart folders, I do not think they will make nautilus any heavier. Since it already can play music files and display images. It would just take up the bar where the Trash: page has the 'empty trash' button.
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