UAC is a method which separates privileges and tasks of a standard user from those that requires access of administrator. While running as a standard account this increases user experience and results in increased security. Now users can flexibly run more tasks, enjoy higher application compatibility without being logged as an administrator which in turn reduces malware affection, unauthorized installation of software, and unapproved changes in system.

So you and all can think of this feature whether it gains popularity or looses. This feature adds some security to Windows Vista and I don't think so that increased security will fail MS.