I'm a dedicated Evernote user. I add just about everything I generate or want to record to Evernote, in one big "notebook", and then I extensively use tagging to make sure everything is findable. I try to use every tag I might ever search for, for which this note would be relevant.
Sometimes I add content to existing notes, if they are relevant and include the same family of concepts. I often merge notes; e.g., I save all my tweets to Evernote via IFTTT, and then merge all of them for each given month.
I often add notes with no tagging at all, and I have a shortcut to search for notes with no tags, as a sort of inbox.
The ability to search everything at once is the key: I can search "movies" or "startup" or "medicine" and find everything with those tags, or those words in the title or text, or even in PDFs. (I use a Fuji ScanSnap to scan documents into Evernote, with fully searchable text.)
The biggest feature I wish for is transcription of voice notes or audio files, so the content would be searchable.
Evernote's Mac app is notoriously slow, but it's gotten better over the years. I still don't understand why they can't make it as fast as the web app.