Many years ago I worked on a similar idea: first a desktop archiver called Dowser, and an online app called Archivd.

If you don't have enough to do (heh) one killer feature is to extract semi-structured data: email addresses, physical addresses, phone numbers, prices, photos, Facebook "og" metadata, etc. Imagine saving a bunch of apartment listings to GimmeBar, and having it automatically plot them on a map of the city.

Good luck!