It seems like the long awaited SP3 won't even see the light of the day. All the patch manpower at Microsoft is now mending the holes in the special sort of Swiss cheese called Vista. And there are a lot of them.

 
Service pack is not just a collection of patches and updates, it's more than that. Whatever was wrong in the initial release can get fixed with the service pack and sometimes you get support for new things with the new SP.

 
With a new another child in the house, Microsoft is treating XP like any evil stepmother would. Abandoning and ignoring Windows XP seems like a wise solution for Microsoft. Vista needs more attention. It is called business what can you do. 

 
If you look closely at Microsofts roadmap, you would see that SP3 for Windows XP was planned for 1H 2008. Microsoft stated that "The date is preliminary" and brings us much suspicion, and not much to hope for.

Link to windowsitpro.