Having toyed with this for a little while and owning a copy of the Beta 2 release, I will say that this "security flaw" is highly overblown. Yes hackers can go in and do ****, but only if you are severly flawed in your mental faculties.
Vista has this "interesting" feature where if you load something that, if changed, will alter the O/S, it will ask you if you are sure. For example, "You are about to load the Control Panel. Are you sure you want to do this? [ Yes ] [ No ]."
Hackers have developed software that just plows into the O/S and tries to take over. In this instance, a box will pop up and say, "You are about to perform X. Are you sure you want to do this? [ Yes ] [ No ]." If you say Yes, then the hacker takes over. If you say No, the program is closed and terminated.
So this interesting "feature" protects the user. It just doesn't protect the stupid ones that will click Yes. There is also the option to turn this feature off. That will also open up the security and enable the hacker to take over.