I don't see what all the fuss is about. We've known that this has been possible for some time now. There were various proof of concept files doing the rounds, and some fool deleted his home folder when he attempted to download a warez version of Office 2004.
It is impossible to completely protect a computer from human error. If you allow a user to install programs, and delete and modify files, then there is always the chance that they will do the wrong thing, and more so if a confidence trickster makes it look like they are doing something innocuous.
The old joke about emails giving instructions on how to see naked Britney pics by typing sudo rm -rf etc. is true. If you can convince a person to do a bad thing by pretending it is a good thing, then no computer is ever safe. All that remains is essentially a damage limitation exercise.
As it stands, Apple has been pretty good about making this sort of thing unlikely. If you download an app with Safari, it will warn you that it's an app. If you run an app indirectly for the first time, you will be prompted to ask if you really want to run it.
What Apple hasn't done well enough falls into two categories.
The first is that they have not been sufficiently informative of average users about the difference between admin and user accounts. Every new OS X installation ought to prompt the new user to set up two accounts: an administrator account (bare bones account) and their actual user account.
I have my Powerbook set up like this. There are user accounts for myself and my wife and a bare bones (no desktop pic, three things in the Dock) admin account. When I need admin privileges, the system prompts me and I enter the admin account name and password. In this case, I would have been immune to the virus, since it would not have had permission to write to /Applications or /Library unless I authorized it. I almost never have to switch to the admin account directly (and fast user switching means that isn't a problem in any case).
In addition Apple needs to alert users to the warning signs of malware. If a file that is not expected to prompt an authorization dialogue, does so, then users need to be educated into realizing that this is a time to stop and think about what you're doing. Frankly, the dialogue should be improved by including a short statement to the effect that, if the file you clicked on was not an application, you ought to stop and check it out (with a link to the appropriate helpfile).
Of course my home directory could still be wiped out, but while that is bad, it is not something that can render the computer inoperable. The former is a very bad day, the latter is likely an irretrievable catastrophe that will destroy everyone's stuff and require a trip to the repair shop or a complete reinstallation.
The second thing Apple needs to do is (as some people have suggested) provide some disctinction in the GUI between applications and everything else. The best and easiest suggestion I can think of is to provide a noticeable highlight to the filename of every application. It doesn't have to be bright red or anything like that, but it ought to be enough to give pause to anyone who sees a jpeg with the glowing writing underneath it.
Doing both of these things would vastly reduce the already small risk that OS X users face. Merely mounting an awareness campaign and highlighting application file names would probably be enough to prevent most idiots (i.e. all of us at one time or another) from being victimized.