I have kept my entire library in Aperture project, and I have kept a backup vault.
Late last year, I went to access my Aperture library and found it to be corrupt - Aperture will not load my library. Attempts to restore the vault have also failed. While I have some JPGs of my Aperture library available on iPhoto, the original RAW files, and much of the collection itself is available only in the Aperture project.
As a last resort, I can probably recuperate the RAW files by manually opening the Aperture project in the Finder. However, I will loose the post processing, sorting, and all meta-data that for the entire library - rebuilding this data will take many many man hours (1000s).
I need to tackle this project soon, and then re-consider my choice for photo post-processing tool, and my backup system.