I use it for all kinds of notes, like for example short tutorials on the command line, issuing commands that are hard to remember, TODO lists (both at work and for grocery shopping), meeting notes, listing pros and cons, everything.
In meetings I like the ability to record audio, or to add pictures I take with my phone, which isn't necessarily a capability of your average open source alternative.
Its search capabilities are also great. I have a ton of notes in my Evernote and I never have issues finding what I'm looking for. Compared with Google Docs for example, which is terrible.
My problems with it is that the data is not easy to port, I would have liked for example periodic Markdown backups to my Dropbox. Also support for encryption is weak. Apps like Evernote can be end to end encrypted, there's absolutely no reason for Evernote, the company, to have access to my notes.
I also worry about Evernote, the company, dying on me like many other startups before it.