Tip 1. "... keeping your computer on the whole day is not advisable." 
It is true that every time you run an application, it eats up some  computer resource. However, it does not necessarily follow that it is  not advisable to run your computer for more than a day. I have my  powerbook's uptime for more than 7 days with no noticeable  performance loss. I do reboot it every 7 days just to make sure that  I keep everything fresh every week but it is not necessary. Linux  users can attest to this as well - I am sure that there are those  people who run computers for more than 2 weeks without rebooting.  Remember that we are talking about portables and desktop computers  and not servers (in which case, we count by the number of months of  uptime!)

Tip 2. Although Mac OS X and Linux are not immune to viruses, its  rock solid Unix core makes it more difficult to infect as compared to  Windows. In fact, I do not run any anti-virus software on my  powerbook and my brother's Ubuntu Linux workstation.

Tip 3. "Auto-Starting Services and Applications."
Ah, this one  applies to Linux more than the Mac. Default installation of some  Linux distributions have some services automatically enabled. It is  not difficult to disable but you have to be conscious of these  services. Disabling unneeded services frees up memory space thereby  improving your computer's performance.

Tip 4. "Device Driver Conflicts."
Same can be said for Mac and Linux.  Frankly, I never bothered thinking about this problem since using a Mac.

Tip 5. "Apply Software Update/Patches."
Definitely a good tip. Unless  the vulnerability is critical, I'd recommend waiting for a few days  before applying the update - just to make sure that it will not  conflict with your existing hardware and software (let others do it  first hehehe).

Tip 6. "Delete Unwanted Files."
Another great tip. Although it does  not drastically reduce the performance of your computer unless you no  longer have disk space for your virtual memory. Mac and Linux users  benefit from monitoring the tmp and cache files, too.

Tip 7. "Run System Utility Tools."
Regularly defragging your hard  drive improves the application's load time and lessens the stress on  your hard drive. Mac users are advised to run Disk Utility's Repair  Permissions regularly.

Tip 8. "Avoid Installing Untested Programs."
This advice goes for all  except for those who live on the bleeding edge. Beta programs does  not necessarily mean that it is not full-featured but it sure is not  production quality since it has yet to go through the quality  assurance process prior to release, i.e. there are a lot of bugs  present! :)

Tip 9. "Clean your Computer Inside and Out."
More often than not,  users tend to ignore this fact. Dust does collect easily near the  computer's fans. Regularly cleaning it ensures that your computer  functions up to spec.

Tip 10. "Upgrade Your System."
More RAM indeed improves the  performance of your computer. Free hard drive space is also important  specially if you are doing a lot of multi-media processing. If you  can afford it, max out your RAM.

So there -- an "extended" list on how to keep your computer healthy. :)