If the choice is between filling my Restricted Sites with thousands of entries on a weekly basis or using Internet Explorer 8, I'd use IE 8. Here's a comment about this issue from the Internet Explorer Blog relating to the RTM release.
http://blogs.msdn.com/ie/archive/200....aspx#comments
IE8 Security Part IX - Anti-Malware protection with IE8’s SmartScreen Filter
Personally, I haven't been using immunize on current operating systems myself for a couple years. The fast-flux networks and other quickly changing location technologies involved in malicious delivery systems today make this relatively slow method of site blocking nearly useless and simply an exercise in update futility.
Since these registry and hosts entry systems were never really designed for automated 'stuffing' of large lists, they've always been limited by the overhead they create. The idea that these lists have no effect on the operation of a system and are in effect 'passive' is a myth that has pervaded the home security community for years. Any 'list' contained within a program will require a finite amount of time to search, regardless of the efficiency of the code that performs it.
However, the real problem here isn't the abused technolgy, it's the valid points made by Eric in his comment that there are much better protection systems now built into IE 8 itself. These systems in some cases don't suffer from the scalability issues that are inherent with locally hosted and searched lists. For example, SmartScreen Filter uses a list which is hosted by Microsoft, to which any IE 8 user can contribute and which is thus much more quickly responsive than a local list downloaded weekly.
Much is often discussed about the limitations of collecting and distributing lists of malicious code (i.e. viruses) and the inherent delay involved. However, few ever consider this same issue as it relates to malicious sites, since these somehow seem less likely to change. In reality though, many of the most prolific malware delivery systems in use today are much more dynamic and thus too quickly changing for such old ideas to work. These systems are best left for the user to perform blocking of individual sites on demand, which was their intended purpose in the first place.
Bitman