Microsoft are distributing Windows Service Pack 1 via Windows update. It is a massive download. On 3 of my PC’s I’ve seen downloads from 550mb to 890 MB.
On all my PC’s it failed after the initial download and install. Clicking on try again results in an additional download and the install then succeedes. It’s like the initial download forgets something.
So far so good after the upgrades. Other than the install glitch the upgrade works well.