Common Scenario: You just rebooted your server after installing updates. You know there are still updates the your server doesn't have installed, but the server isn't pulling them down from your Windows Server Update Services (WSUS) server. There's not enough time in your maintenance window to go to update.microsoft.com and download the remaining updates, that's why you have a WSUS server in the first place right?
On Windows XP and Windows Server 2003 you can force detection by running the command:
You won't see any immediate results, but within a few minutes the familiar yellow shield should show up in the notification area informing you that updates are being downloaded or that updates have been downloaded and are ready to install.
Even though I'm fairly up to date with updates in my system images and Microsoft Office installs, I still try to run this after imaging a system or installing Microsoft Office just to make sure nothing was missed before handing things over to the customer.