And yet other, perhaps worth a thread: I understand that there really are some viruses for Linux, albeit most of them do not roam in the net. Is it an actual possibility to catch one of them? Should a Linux user do something as a precaution?
There are virtually no Linux viruses found in the wild. For safety, use a firewall, and possibly run a rootkit checker periodically. Make sure you stay fully patched. And, just like any other OS, don't get suckered into running something you shouldn't. E.g., looking at a dirty picture shouldn't require root/execute permissions.