Safari, Chrome, all the non-Windows phones (iOS, android, bada, blackberry, and webOS) and some lesser uses. I think some of the embedded Netflix implementations use it.
Apple paid someone to hack on KHTML (In a most unfriendly manner) and Safari somehow becomes some of the most important code on the planet? Apple fans are a bit delusional.
If Safari magically disappeared today Mozilla would notice a bump in downloads and everyone would go with their day.
What exactly is your argument, that it's not important because people could use something else if they had to? Does anything qualify as "important" with that definition?
There seems to be some confusion about what "it" refers to. You keep referring to Safari. The original poster referred to KHTML, which for most intents and purposes "turned into" WebKit. That's how I and apparently most others understood him to mean.
WebKit, the rendering engine originally used in Safari (not Safari the application), nowadays powers Chrome, iOS, Android, BB and a hundred other browsers/platforms. In simple words: the absolute majority of mobile browsers use webkit, plus >50% of desktops/laptops.
It's pretty important.