- Antivirus? You don't need that, virus threats are nearly inexistant in Linux. I never had to use any antivirus and I've run Linux since 1996
- Syware? 90% of your software is open source .. so no spyware in there, and most of your proprietary software comes from the repositories, or some other trusted source. It happens now and then (for instance people are doubting about SKype and the reason why it would go and read Firefox passwords.... ) but it's never a big thing. The community itself is the best anti-spyware you could ever install
- Checkdisk? This is done every 30 times you boot your computer at boot time, it usually doesn't take to long.
- Defrag? No need, the ext3 filesystem is journalized.
- Security Upgrades? This is a very controversial subject, and with Celena disabling the update manager we're heading right towards big controversial talks. My advice? Don't take them... they fix security holes but also introduce bugs, I prefer stability to security. Especially with more than 2 releases a year... you don't really need that.
- Registry cleaning? There's no registry. I suppose you could clean Gnome's gconf registry now and then.. but again nobody does it.