I'm trying to understand how Spybot immunization works. I've read the thread where some answers where given but I'm not happy yet. I see the modification of the hosts file and how Firefox and Internet Explorer sort of cannot reach the domains no more. My question is simply, why do I need more protection than that?

I feel that my system gets kind of bloated when immunizing Internet Explorer through the registry. Not that Windows would get any slower or anything but, TuneUp Registry Defrag reports a size of 12mb right after installing Windows and after installing Spybot and immunizing IE I have a registry with a size of 22mb. Is this really really necessary to stay fully protected?
Right now I see the HUGE list of domains found in HKEY_CURRENT_USER\[..]\Internet Settings\ZoneMaps\Domains having duplicates all over my registry. Gosh this seems so wrong?

Is it correct that Firefox immunization is only done in permissions.sqlite (And of course hosts)? This is great. Having only two files go from 2kb to 1.5mb is in my opinion a better way than doubling the size of the registry.

I see a different behaviour after immunizing Firefox and entering for instance 008i.com than after having only the hosts file modified. When only hosts is modified I end up on a "This domain me be for sale" page, but when Firefox has been immunized I cannot reach the page no more. This would to me be the expected behaviour having only hosts modified. But has that got anything to do with that www. 008i.com isn't in the hosts list and just 008i.com ? :S This is the case of quite many domains listed. Why? Isn't 008i.com kind of just redirecting to www. 008i.com, thus modifing hosts has no real difference? (This is why I wrote "sort of cannot reach" in the beginning )