If you are using Dropbox at work, there is a good chance that you don’t want to download content from all of your folders. Some of your Dropbox folders could contain personal data, or items inappropriate for your particular workplace. To avoid problems arising from this, we can use Dropbox Selective Sync. Selective Sync will keep your data backed up in the Dropbox cloud, but it will prevent a particular computer from downloading the files you deem unworthy.
What is Selective Sync exactly?
By default, Dropbox is set to sync all of your Dropbox folders to your computer. You can change this using Selective Sync during installation of Dropbox, but you can also change it later on. Selective Sync does exactly what it sounds like. It lets you select which folders from your Dropbox cloud-storage that you would like to download to a computer that is synced to your Dropbox account.
As said, this can come in handy for work, but it could also be useful for numerous other situations -such as school. Or, perhaps you have one particular Dropbox file with 10GB+ of files in it, and you really don’t need to sync that; you can just turn off the one overstuffed folder!

Ready to set it up? Let’s do it!
Step 1
Assuming you already have Dropbox installed and running, Right-Click the Dropbox icon in the taskbar. From the menu that appears Select Preferences…
Step 2
In the Dropbox Preferences window, Click the Advanced tab and then Click the Selective Sync… button.

Step 3
Here is the fun part. Go through all of your Dropbox folders and only leave Checked the ones that you want to download. Any folder left unchecked will remain on the Dropbox cloud and will not be downloaded to the computer. If a folder is already downloaded, un-checking it will delete it locally from your computer, but it will still persist online in your Dropbox account.
Step 4
Dropbox will display a confirmation message just to be safe. Click OK to save changes.
Done!
Now you have Selective Sync set up on your computer. You’ll have to repeat this process for every computer that you want to set Dropbox sync up on, but you probably want to customize it differently for each one anyway.

That’s it folks… MacLitigator all outta ivtines. If anyone else wants an invite it’ll need to come from a prior commenter.
Thanks for the info,
So my understanding is that you can prevent remote files from synching down to your local computer. What about the opposite direction? What if I add local files that I don’t want to sync up with the server? Do you know if that’s possible?
just wanted to say thanks…been looking for this precise info for the past half hour
What happens when the folder you unceck has files that are not syncronized with the cloud?
They will be removed from that computer ASAP. They will not however be removed from the cloud or other pc’s or devices.