Isn't this sort of a myth? I run Linux and a virus running as my primary user (non-root) could delete every single thing I value on my computer.

I assume the same is pretty much true for OSX.

The problem with building a virus on OSX is not obtaining root access, it is replication. How is a virus going to propagate from one mac to the next?

If you don't propagate you're just a trojan and will have limited penetration.

Yup, for most people, the thing that most needs protecting is the data, not the apps. But the important thing to note is that if the malware can't install itself/access hardware (esp. the network interface), then your platform is not very interesting for malware writers.

Of course, I should point out that the person you were replying to was exactly back-to-front. It's much easier to wrangle a privileges escalation than it is to get onto the system in the first place.

Yes but you have backups of that stuff. The real threat/pain is your machine becoming a spam/etc zombie without your knowledge. This is highly unlikely on any Unix-like OS.

If it's not tough, then why hasn't there been one yet? A trojan is easy, but a trojan is not the same as a virus.

Erasing my home directory would be plenty of damage.

The hard part is propagating to other computers.