For reading a single thing later, I use Instapaper: http://www.instapaper.com/
For bookmarking links (and sometimes making notes) I use Pinboard: https://pinboard.in/u:wpietri
For following RSS feeds, I use NewsBlur: http://newsblur.com/
If it's relevant to an upcoming task, I'll paste it into a note on my task tracker: http://kanbanflow.com/
And then when I'm working on a specific thing, I sometimes keep a journal in Evernote and paste in notes and links.
Other than that, I've stopped tracking things. My natural inclination is to hoard information. I've mostly stopped doing that, trusting that if I really need to know something I'll be able to find it again.
(1) Insights and Ideas. The reason these are valuable to me is the thoughts they provoke in my head. I try to make most insights I come across "mine" by writing them and the ideas they prompt in a memo to myself or even simply on an index card. Of course, I always record the source, even if I don't record an exact quote, to avoid plagiarism if I use these notes in something published. I also have a computer file of quotes on various subjects. These are usually either humorous or wise rather than topical.
This process is much more time consuming than slurping them into an electronic storage system, but for me, the cost associated with this technique is a feature. The "friction" involved in pondering and writing about ideas forces me to be discriminating and not waste my time thinking about or storing ideas that aren't valuable to me. Perhaps other people don't need this discipline, but it has made me more productive than when I have used tools optimized for rapid storage.
(2) Code. Functions or programs that demonstrate techniques or features go into a well-named file in a directory reserved for each language or product I work with.
(3) Facts and formulas. I don't record many of these, preferring instead to have (or have access to) good references material, but when I do, I either print the source, or write them myself on an index card and store them in a paper file per subject.
1. For one-line stuff (url's, names, whatever) I use Wunderlist so I can process it later on my mac.
2. for interesting articles, I currently copy the URL and open Instapaper, which then offers to add the url on the clipboard.
3. For snippets of text, paragraphs, whatnot, I use PasteBot. Usually copy/pasting this text will give me the link at a later time. I then process everything in there once a month or so.
Why I like diigo -
1. Available everywhere - they have good, working extensions for popular browsers, native apps for mobile
2. You can highlight and annotate parts of web pages and if you visit that page again while logged in to diigo through the extension, it will show you your highlights/annotations
3. Tagging & bookmarking (I switched from delicious while it was in future:uncertain state)
4. You can create groups and add links to groups (e.g. I use this feature to share links and my comments with my wife on topic we are concentrating on/discussing)
5. Share feature. Very easy to share a link and a quick note to anyone with email address
6. It has other _social_ features (share on twitter/facebook, etc.) but I don't use those
I am not affiliated with diigo in any way. Just a happy user.
Pinboard for links, including articles I might want to read later. I have archiving on so that I don't lose any useful references. (This is by far my biggest store, and I'm still working out my tagging taxonomy.)
Evernote for notes relating to projects in progress, including any notes I'm taking while learning a new technology. (Project-related to-read links usually go here, not Pinboard.)
nvALT (Notational Velocity fork) through the Simplenote API for more permanent notes: lists of things, useful command line tricks, music to check out, etc. (Google Docs used to be my place for this, but nvALT is WAY easier to use.)
Wunderlist for specific to-dos related to my current projects.
This approach only works for web documents, not for web apps. I don't really use web apps much, but if you do, you could consider using bookmarks or something.
For the longest time, I had issues finding a good workflow with Evernote. I purchased and read Bradley Chambers' e-book on Evernote and have been using Evernote comfortably for several months now.
I can clip individual images, the whole page, a selection of text, or just a screenshot.
Personally, it looks like saves entire web pages which isn't exactly what I'm looking for (though you seem to recognize that).