I 'installed' it from Software Update.
Nothing changed. Boot ROM is the same as before.
After, I went and downloaded it from the Apple support site.
And it's 'not supported' on my machine, which is Apple speak for 'it's already installed.'
Installed the update without a problem on my 27" i5. I hope this will fix that "scrolling stops working" issues I noticed in in several apps (twitter & reeder) or at least my video stops playing issue which I could "fix" with a four finger swipe to the next space.