May I nuance a little bit...
there is a diffrence between using the Aperture Library and using the Aperture Vaults!
Not using the Library is a little foolish because that is what makes Aperture ...well.. Aperture!
Not using the Vaults is an option that has pro's and con's.
I have been using Aperture since december 2005.
At first... I used Vaults.... after 2 month I emptied (deleted) all the Vaults.
There is no diffrence at all noticable.
Only when I will be in desperate need of an instant back-up ... then there will be a diffrence.
Correct me if I am wrong!