Things I have noticed with SP1.

SP1 has greatly reduced the time it takes to calculate file copies. It has also increased file copy speeds, local machine file copies, and copies across a Local Area Network. ex - Copies from my desktop to laptop would usually go about 1.5 MB/S via wireless G. After both machines updated to SP1 the same files go about 2.4 MB/S. I have not compared wired speeds.

Things seems a tad snappier with SP1 installed on my x64 and x32 systems (Desktop and Laptop).

SP1 also seems to keep your custom folder views intact (so far). My pre SP1 systems would occasionally reset folder views back to default.

The 2K8 Kernel is a good thing. I'd imagine it is more reliable than a desktop varient.

SP1 seems to report memory values differently than RTM. ex - In my computer, it used to report 4096 MB Ram, now it says 4.0 GB RAM.

I have never received a BSOD in Vista (when I wasn't overclocking). So I can't speak about reliability as it applies to the release canidate. But I can say that none of the applications I was using, have stopped working.

My only complaint is x64's ability to cope with unsigned device drivers. With a new hotfix, and SP1 I'd imagine, you can not use the DDISBALE BCDEDIT trick to stop driver signing requirements.
However, last time I checked, the setting to disable driver signing in gpedit is still there, but no longer works

User Configuration -> Administrative Templates -> System -> Driver Installation

"Code Signing For Device Drivers". It no longer works, and the last part of the description is incorrect. There is no "Driver Signing" button in the hardware tab anymore.

Please either make this setting work, or remove it, I don't like be tempted with settings I can't change.

-Brian