If this is the WGA authentication stuff, I believe it does 3 things that are noticable to the user if they own a pirated version of windows:

First off, when you boot, your windows login page will display a message that says:
'You may be a victim of software counterfeiting. This copy of Windows is not genuine and is not eligible to receive all updates and product support from Microsoft.

Click Get Genuine now to get more information and resolve this issue.'

Then, secondly, you will have a notification icon in your system tray that will display a validation error every so often.

And then lastly, if you selected to 'resolve later', when you lock your desktop, you will get the following banner text when your computer is locked:
This copy of Windows is not genuine.
You may be the victim of software counterfeiting

There may be more stuff under the hood, but I haven't read any besides that PC's that fail the WGA, will only be able to get critical updates from MS and nothing else.

Also, you cannot uninstall and disable the WGA by using the Add/Remove Programs. It will allow you to view Windows Genuine Advantage Notifications, but you cannot use Add or Remove Programs to remove the notifications.

You can also temporarily disable Windows Genuine Advantage Notifications. To do this, right-click the Notifier icon in the notification area and select Change Notifications Settings. Then, follow the prompts. This will disable the Notification Prompts until a new release of the Notification Update is released.