Absolute privacy on Facebook (and the Internet) is an illusion, it doesn't really exist. Relative privacy is the best that we can hope for.
Should we panic about this?
There's is a very simple solution. If you absolutely don't want to share it, then don't upload it to a SOCIAL networking site.
And fortunately, most of the people that we've surveyed, appear to have enough common sense to understand the costs and benefits of sharing.
P.S. It would, however, be nice if Facebook users could disable the share with anyone option.
We haven't seen it in the wild, but it would be rather trivial for a worm such as Koobface to collect such URLs when an account is compromised. Recovering the account and resetting the password won't invalidate access to these links.