I am confused!

[Oki]

Hi, I am trying my best to learn and use Ubuntu Linux, and I really love this OS. I will stick with it, no doubt about that. But I have been a little confused lately; there are mixed information out there. So if someone could comment these 4 questions I would appreciated it!

1:
I hva been told that I dont need a defragmenter for Ubuntu Linux, cus etc3 fix this for you every 15 times you boot it. This is one of the goodies with Linux that I have told others about:
But look at this: http://ubuntuforums.org/showthread.php?t=169551

2:
Then I have been told(read) that Ubuntu Linux is more safe since you log in as a user, not as a super user. So if you got a virus or trojans, they cant install themselves in other places but the users space.
But you can read this regarding Mac witch has the same system; “this program could be silently installed to your User account and hooked to each application you use… and it doesn't require Administrator rights to do so.” Link; http://www.f-secure.com/weblog/archi....html#00001030
So, if this can happened to Mac OS X, then I dont understand why it cant happened to Linux – both normally requires password/sudo to install something?

3:
Then I have heard several times that I dont need any anti spyware/trojans programs under Linux, cus there aren't any. But I have a book about Ubuntu, witch has a guide on how to install anti spyware program for Linux, and recommended it.

4:
I have also heard that Linux needs less CPU then Windows, so shifting to Linux will be good since your applications can run faster. But I must say that I dont feel Ubuntu runs any faster then Windows XP when I am editing photos, writing in OOo and so on...

I am not whining, I am only wondering about those subjects – and I dont want to tell others wrongly about Linux. I will stick with Ubunut, I am really happy with it - but hate to be confused