It appears that it "should" be released around October/November.  I have been doing some research about Vista UDP/IP lagging, which negatively affects online FPS gaming.  I noticed some of my online sources have subsiquently been scrubbed of info that it's the Vista networking stack that is at fault.  It seems M$ would have you to believe it's the 3rd party video drivers that are at fault, certainly not it's much ballyhooed Vista networking stack!   

Anyway, this article mentiones that M$ is tight-lipped with what is in the SP1.  I bet, once SP1 is released, the online gaming problem will mysteriously be fixed!  Why, (sarcasm alert) because M$ will claim it included in it's DX10, a fix to make up for the shortcomings of poor programming on the part of the 3rd party video driver manufactures!

http://vista.blorge.com/2007/04/21/intel-confirms-vista-sp1-release-date-for-mic...