Yeah, I can see how making a virus for Linux would be seen as a waste of time. Not only due to the small user base, but also because, clasically, Linux-users are heavy-duty geeks, and they have computers built like a bank safe. Hopefully no one catches on that dummies like me are now able to use Linux.
Linux is indeed a target for authors of malware. Certainly, not as popular as Windows, but it isn't immune. I've worked on a system that was infected with a rootkit. It was primarily a web/mail server, and we had SSH open for remote administration. Somebody exploited a weak password (we concluded, but no way to know for sure) and hosed it pretty good. There are various reasons why Linux is a more difficult target, but it isn't an impossible one by any stretch, and as it gains in popularity, there will be more attacks. So Linux users need to be just as vigilant. Certain distributions were regularly criticized in the past for poor security out of the box. RH, for example, would by default start up too many services -- I think they've stopped doing that. Ubuntu, out of the box, doesn't come with the firewall enabled. (I haven't upgraded recently, so I don't know what's in the last couple releases.) This didn't bother me, because I'm used to configuring it by hand, but novice users won't know how, or even necessarily want to learn the gory, command-line methods. If you're a Linux user, make sure you have Firestarter or something like that installed, and learn some basics. Find a local Linux User Group for tech support. If you're an advanced user, and/or more paranoid, install Bastille. And keep up to date on patches. I'm more than a year behind on the release of Ubuntu I'm running, but I am completely up to date on security patches.
Also, for gaming on Linux, there are now some great games to run natively. And in addition to Wine, you can spend some money and get an enhanced Wine call "Crossover", I think, that has better emulation. But that's a topic for the Lounge, or maybe a Linux user's social group forum. I enjoy running the arcade Galaga using MAME -- it's just so retro-cool!