If you sign into your Dropbox account online, you'll see a "Sharing" link on the left side of the page. Click it, and you'll see a list of every Dropbox folder that you share with others.
I've been using Dropbox shared folders for a while now, and it finally occurred to me that I should probably review them. Sure enough, I found several that I needed to unshare. So I did.
Projects come and go, computers come and go, and relationships among people and teams change. And you know what? You're under no moral obligation to continue sharing any folder indefinitely.
I say, if the need for a shared folder passes, you should severe the sync. Every shared Dropbox folder is an opportunity for someone to add or delete data from your personal hard drive. The more shared folders you have, the more opportunity for (usually inadvertent) bad things to happen.
One time someone accidentally copied a few hundred megabytes of their personal data into a Dropbox folder I shared with them. All that stuff ended up on my hard drive. Ick.
But this is hard, right? I mean, it probably involves a bunch of fiddly, arcane settings, so I'm going to go back to Twitter now and turn my brain back off, OK? OMG, Honey Boo Boo is @replying!!!
No, stop that. Unsharing is really easy. Just click the "Options" link next to a folder you want to unshare. You'll either see an option to unshare, to leave, or both. I'll explain.
Unshare folder. The unshare option shows up if you're the original owner of the folder and shared it with others. In this situation, you'll also be given the option to let other members of the shared folder keep their own copy of the data. If you choose not to let them keep a copy, the contents of the shared folder will be permanently deleted from their computer.
And yes, I mean permanently. The data won't even be recoverable through Dropbox's standard undelete feature. I'm sure there are situations where this might make sense, but I would generally recommend letting people keep a copy.
Leave folder. You'll see this option if someone shared the folder with you. If you choose to leave, you'll be given the option of leaving the contents of the folder on your computer or removing it right then and there. If you choose to keep the data, the folder simply turns into a normal Dropbox folder. All future changes are synced to your Dropbox account only.
If you created a folder that's been shared with two or more other people, you'll see both options above. As the owner of the folder, you can choose to unshare it, which ceases all sharing for everyone, or you can simply leave the folder yourself but keep sharing intact for the other members.
Folder owners can also assign other members as owners and even kick out individual members. By the way, all of this is explained really clearly and well-illustrated in Dropbox's help system.