Agreed. It takes <60 seconds to back-up all my personal files to a reformatted USB3 thumb drive I can stash in a safe. I only ever use them from one PC. Dropbox is good for collaborating but I think the "use from any device" benefits are a little bit overplayed. How many PCs and cell phones do people really do work on?
I have a desktop and a laptop that I use regularly, plus a work laptop. And I teach in a classroom that has a PC in it, so I regularly access Dropbox from 4 separate machines, not counting mobile devices.
Many people don't even know you can plug in a thumb drive on a phone or tablet, so if you're going to transfer files back-and-forth between just two devices, you pretty much need a syncing software.
It's funny, until I read your comment I didn't realize I would ever actually consider buying flash drive again.