For web stuff my criteria is pretty simple. If I'm looking for this information a month from now and I search for it via Google/Bing, will I find it in less than a minute? If not, I save it if I consider it something of longterm value. For web pages I bookmark, for articles I want to read I save to Instapaper.
In general I tend not to save stuff. The web isn't going anywhere so there's no need for me to store it (or save links to it) locally. There's now so much good information out there that you can usually re-find what you're looking for (or something very similar) pretty quickly.