Mostly I save ideas for projects or personal development things that I need to do a more "deep read" of (this also allows me to tag it for that purpose, and when I want to go back to something I've worked on I can find references I've used for specific projects that I may not have saved elsewhere), things I've read that I might want to reference later/thought was a good read or interesting and tag it with the relevant stuff. Mostly I just use it as an instapaper backup, where I have it automatically save my Archived stories and it tags it with a "tagme" tag that I go through once a week or so.