It's no secret that there's a leaked beta of Vista SP1 floating around, but no-one yet has really taken the time to analyse it in detail to find out what it really does.
I made it my mission this weekend to trawl through the registry and file changes in SP1 to find out as best I could exactly what SP1 does.
First up, I can say that there is a very noticeable performance increase. It is obvious that since Microsoft released Vista to manufacturing, it has been optimising the code ever since. (I suspect this revelation will fuel the fires of the people who say Vista was released before it was ready for prime-time.) There’s far less hard drive thrashing and in general the system seems much smoother and more responsive.
Amusingly, the build of SP1 we saw (which in this beta comes fully integrated into a 3.2GB Vista install DVD, rather than as a standalone update) still has Microsoft's internal network shares embedded as the source of the updates. For example:
Not that that info is really useful to anyone, but it mildly tickled our curiosity bone (next to the funny bone) to see the file layout of Microsoft's internal distribution shares.