Hey guys,
I helped build this feature and just wanted to say we're as concerned about privacy and security as you are. A couple specifics that might help:
* No feature is for everyone -- this is opt-in in the strictest sense. (And, since you pick the files/directories, as fine-grained as you want.)
* You can disable a link anytime: from the the sharing tab (https://www.dropbox.com/share), click "Linked Items" to see all your links and disable anything.
* 3 means of sharing (shared folders, a public dir, and sharing links) gives you more control over privacy, not less.
* Similar to etherpad links, the shortened db.tt links are public but unfeasible to guess. We've heard a few concerns about the 6-digit hashes -- well, as more links are shared, don't assume the hash will stay at 6 digits :) can't get into details but we do a few more things to make link fishing near-impossible.