Absolutely no installation problems here! Installed via Windows Update download.
First you get this screen:
Then agree to the usual licence:
Then Vista warns you it could take over an hour or more and you can't use your PC while you're waiting:
At this point just before clicking on "Install" I disabled or exited all background applications that were running in the System Tray, via the "Exit" or "Close" options in their icons, including my Anti Virus application. All that were left visible were the "Windows Updates" icon and the standard volume control/Networking icons. I don't whether this helps for a safer or easier SP1 installation, but it can't do any harm!
Then Windows proceeded to continue the download. First part took about 10 minutes to download just the necessary parts of SP1 I guess. Then a reboot during which the PC went through the 3 stages of the installation over about 15 minutes. Then a normal startup of Vista with about another 15 minutes of major "disk churning" before it finally settled down.
The I went into Windows update and the Welcome Center to find all is okay:
No software or hardware issues at present and system seems overall "snappier". So far, I'm impressed!