Microsoft's XP SP3 release manager Chris Keroack has announced that the long awaited Service Pack has been released to manufacturing channels and will hit OEM and enterprise customers by April 29th.
On that day the SP3 will also be available for download from the Microsoft Download Center but it will be an optional download, most likely in response to the company's recent debacle with the release of Vista SP1.
The key features of Service Pack 3 are "Microsoft's updated Management Console 3.0, which appears in Windows Server 2008 and Vista; the new Windows Installer 3.1; an update to Wi-Fi protected access; and support for Network Access Protection, the "health checking" component used by Windows Server 2008."
The official SP3 feature list is available here: Microsoft XP SP3 update list