As you can see from the accompanying screen shots, there just isn't all that much to see yet: Windows Vista Service Pack 1 (SP1) functions like a traditional Windows service pack, aggregating previously released fixes and adding just a few features, none of which appear to expose themselves in the UI. Will there be more palpable changes later in the SP1 beta? Possibly. But Microsoft has been very careful to lower expectations, noting specifically that SP1 will not include a new Media Center version, for example.
So what is here? Basically, the SP1 setup process is an agonizingly long affair, at least using the interactive standalone install process depicted here. (So-called express installs should be similar, albeit with some online component downloading.) I will examine slipstreaming in the future.
In any event, an interactive install requires several reboots--five, if I counted correctly--and a surprising amount of time. When all is said and done, what you're left with a system that's apparently visually identical to the one you started with. It's too early in the SP1 development cycle to worry about such things as performance and reliability, but so far so good. I'll have more reports on Vista SP1 as new builds are released and more information is made public.