If you check the exciting news about the growth of Windows
Vista, you can see a new security feature called User
Account Protection (UAP).
One of the big lack of all the previous Windows family (and absolutely the
big source of Windows problems) is that when you set up Windows, an
administrator account for the user is created. The major part of normal users
works with accounts that have administrator privileges and spyware, malware and
other malicious software are so happy... 
The main reason for this is summarizable on this fact: if you are using a
lesser privileged account, every time you need to install a software, doing an
update or perform a task that needs administrator privileges, you are
forced to logout from your system, login with the admin account and perform the
task. A big noise...
Now Vista introduce this new User Access Protection feature: when a
user runs with a lesser privileged account and needs to perform a task that
needs administrator privileges, the system
will immediately prompt him for administrator's credentials.
You'll see a message like this:
and you can easily login as admin, perform the task and return to your
previous credentials. Wonderful? 
Now the considerations: I've lost the number of times I've talked about this
feature in the past and I've requested it, this was one of the most requested
feature from the time of Windows NT I think... finally we've see the light
with Vista. Was this so hard to implement?
This is a feature that every other non MS operative systems have from the
prehistory (just think to Unix) and I'm surprised that we'll see this only on
Vista and publicized like a "revolutionary" feature. This is a base feature, a
must to have on every OS.
However, nice to see that (with a little delay 
) Microsoft has joined the
"less privileged account" train...