I had a problem with a small group of computers which I deployed in my organisation.
The computers were deployed through images which I created with DriveImage XML.
All went well but I forgot one small step which I will explain later. The computers didn't show up in WSUS but did get their updates from the wsus server I was puzzled.
Then it hit me I did nog give the computers a new sid!
This explained why they did get their updates but did not show up in wsus except for 1. On the systinternal site I grabbed the utility NewSID v4.10 and gave the computers a newsid.

However they still didn't showed up in WSUS. But I found the solution here Athif Khaleel's WSUS blog:

@echo off
Echo Save the batch file "AU_Clean_SID.cmd". This batch file will do the following:
Echo 1. Stops the wuauserv service
Echo 2. Deletes the AccountDomainSid registry key (if it exists)
Echo 3. Deletes the PingID registry key (if it exists)
Echo 4. Deletes the SusClientId registry key (if it exists)
Echo 5. Restarts the wuauserv service
Echo 6. Resets the Authorization Cookie
Echo

This script will force the Update Detection from Automatic Update Client to check for updates on WSUS Server.

Copy and Paste the code below into a text file and name it AUForceUpdate.cmd
=======================================================================
@echo off
Echo This batch file will Force the Update Detection from the AU client:
Echo 1. Stops the Automatic Updates Service (wuauserv)
Echo 2. Deletes the LastWaitTimeout registry key (if it exists)
Echo 3. Deletes the DetectionStartTime registry key (if it exists)
Echo 4. Deletes the NextDetectionTime registry key (if it exists)
Echo 5. Restart the Automatic Updates Service (wuauserv)
Echo 6. Force the detection
Pause
@echo on
net stop wuauserv
REG DELETE “HKLM\Software\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update” /v LastWaitTimeout /f
REG DELETE “HKLM\Software\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update” /v DetectionStartTime /f
REG DELETE “HKLM\Software\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update” /v NextDetectionTime /f
net start wuauserv
wuauclt /detectnow
@echo off
Echo This AU client will now check for the Updates on the Local WSUS Server.
Pause
=======================================================================

Regular TLA reader Chris Sanders has contributed the following list of frequently asked questions about WSUS.

Windows Server Update Services Q&A

I have deployed several WSUS servers in networks of all sizes. This Microsoft technology is one that I believe is a necessity for any network that includes Microsoft servers or clients. Unfortunately, I still see a lot of network admins who don’t deploy it just because they have misconceptions about it. The purpose of this Q&A is to address some of the most common answers I get from those who are looking to deploy WSUS.

Q: What is WSUS?

A: Windows Server Update Services, known as WSUS, is a technology that runs on Windows Server 2003/2008 and allows network administrators to distribute and manage updates to Microsoft products.

Q: How much does it cost?

A: WSUS is provided FREE of charge. However, it does require a server operating system to run, so you must have a valid license for that operating system, as well as Client Access Licenses (CALs) for each computer being updated by the WSUS server.

Q: What products will it update?

A: WSUS will manage updates for virtually every Microsoft product. This includes the Windows Server 2000, 2003, 2008, and Small Business Server

The final version has been released:

Windows Server Update Services 3.0 SP1 - download here.

Quote:

Overview
Windows Server Update Services 3.0 Service Pack 1 (WSUS 3.0 SP1) delivers important customer-requested management, stability, and performance improvements, while incorporating further enhancements to local publishing of drivers and the Client Servicing API addition.
WSUS 3.0 SP1 delivers new features that enable administrators to more easily manage and deploy updates across the organization. This package installs both the WSUS 3.0 Server and WSUS 3.0 Administration Console components, for all Windows Server 2003 SP1 supported languages. Additionally, the WSUS 3.0 SP1 client is included in all supported client platform languages. You must install the server components on a computer running Windows Server 2008 or Windows Server 2003 SP1 or later. You may install the Administration Console on a remote computer running Windows Server 2008, Windows Vista, Windows Server 2003 SP1, or Windows XP SP2.

Supported Operating Systems:
Windows Server 2003 Service Pack 1; Windows Server 2008