XP's 3rd (and final) Service Pack was back in November of 2006, so let me refresh your memory: In January 2006 Microsoft announced it was delaying SP3 to 2007. In April of the same year, Microsoft CEO Steve Ballmer said Microsoft was considering releasing Windows XP SP3 before Longhorn (now Windows Vista) shipped. Windows Vista was at that time expected to ship in the second or third quarter of 2006. Towards the end of 2006 Microsoft announced it was further delaying SP3 till the first half of 2008, also noting that this date is preliminary.
Some people are now suggesting that Microsoft may drop SP3 completely, and offer a last 'update rollup', the same way it did with Windows 2000: At the end of 2004 Microsoft announced it would cancel SP5 for Windows 2000, and issue an update rollup instead.
Although Microsoft is denying any such plans, it wouldn't surprise me if this would in fact happen. It's now over 31 months after SP2 was released back in August 2004, and the stated end of mainstream support for Windows XP is April 14, 2009.
Microsoft is saying that it wants predictable operating system releases, but it doesn't think the same should apply to service packs. On Microsoft's Service Pack Road Map web page it reads: "Microsoft continually works to improve its software. As part of this effort, we develop updates and fixes to recognized issues and release them for customers. On a regular basis, we combine many of these fixes into a single package and make the package available for installation". Sounds nice, but the reality with Windows XP (its most successful OS to date) is quite different. SP2 for Windows XP was released two years after SP1, and we're only a few months shy from the three year mark since SP2 was released. , Microsoft also declined to release an "update rollup" as an interem 'fix' untill it releases SP3.