Em Microsoft Technet , ele diz que você nunca deve desabilitar o UAC e os usuários devem ser executados como usuários padrão ...
Users should always run as standard
users with the following exceptions:
The user travels frequently and may
need to install applications or print
drivers while traveling.
The user uses applications that
require administrative privilege and
that an application compatibility
database cannot correct.
Make the primary user account a
standard user account. For users who
are allowed to perform administrative
tasks on their client computers,
create a local administrator account
for performing those administrative
tasks. When a user is logged on as a
standard user and attempts to perform
an administrative task, the credential
prompt is presented. The user must
enter an administrator user name and
password, and then click Yes to
perform the task.
When users are logged on as standard
users and need to perform
administrative tasks, they can also
quickly switch between the two
accounts by using the Fast User
Switching feature. Fast User Switching
is a feature in Windows that allows a
user to switch to a different user
account without closing programs or
files first. The user can quickly
transition to the administrator
account without disrupting their
current activities.
Aqui está uma boa postagem em Por que você nunca deve desabilitar o UAC
A conclusão é que, se você quiser tornar seu Windows mais seguro, deixe o UAC ativado e execute como um usuário padrão.