As far as my experience goes, the answer is "yes" for Dropbox - your account will show "1 GB over quota" (and syncing will stop) in this case, as shared folders

As far as my experience goes, the answer is "yes" for Dropbox - your account will show "1 GB over quota" (and syncing will stop) in this case, as shared folders count toward the quota both for you and the person who shared it with you. Many moons ago, Dropbox promised this will be changed, but it has been on hiatus ever since (my guess is on slightly larger profits and drastically simpler quota accounting).