I used to use Yojimbo, but I moved to Evernote for better syncing.

I use it for a combination of things, but mostly as a place to put and file things I might want later.

I store articles I find on the net, and download the full-version of them, with the Evernote Web clipper. This replaces Pocket, and other apps, and allows me to have synced versions on my phone.

I store Dungeons and Dragons Gamenotes, and have thema cross whatever laptop I happen to bring to game. I GM, so there is a lot to keep track of.

I keep recipes that I yanked from my Mom and Grandmother, so I can type in "cookies" and quickly find how to make them.

Basically, I use it for any content that I want to save, sync, and search.

Could I use The Filesystem+Spotlight+Dropbox? Probably. But the finder's UI has to do a lot. This has a UI which is dedicated to my use-cases. For me, it makes a lot of sense.

I'm a college student, so I use it to take notes in all of my classes. Since it all syncs between devices and I can access it from the web, I have access to my notes wherever I am and with any device I have. It makes my life easier because if I'm going to the library to work or meeting with a group to work on a project, I don't need to lug binders or even my computer around. The photos feature makes life easier as I can just take pictures of whatever is on the board.

I use it as a personal wiki, mostly text. Whenever I researched something that took some time, or finished installing a particularly difficult type of open source software on a weird platform, I save all my documentation with links, etc here.

I (try to) use it for storing and organizing stuff that I would otherwise organize with the file system.

Evernote is better than the file system/Dropbox primarily because it does full text search of PDFs (even scans), words in photos, and plain text.

Evernote also lets you look at all file types in the same interface. And there are good mobile apps.

It's sort of like an integrated version of Spotlight, Quick View, and Dropbox but with better search and better mobile apps.

Paperless. I scan and classify in Evernote every single mail I receive. (tax, invoices, gvt mail, etc..)

I use it for my weekly to-do list (since it then syncs across all computers and my phone), and it is a convenient way for me to keep track of my different projects. I type up a short summary for myself after meetings and I can also easily take a photo of a blackboard and include it with the notes. It's also a decent way to quickly record addresses or library call numbers, and to draft e-mails to send to my classes. (A proper e-mail client would work for this last purpose, but the only reliable way to e-mail all students in a course is through Blackboard, which is uniformly terrible.)

OCR allows me to search any image I throw at it.

I use it as my virtual printer.

Every online receipt or payment confirmation, flight details, etc gets inserted into evernote via OS X's "Save PDF to Evernote" link in the print dialog.

I hardly ever look at the stuff, but it's nice to have it all indexed and immediately searchable.