Apple-backed WebKit is the open-source rendering engine behind Mac Safari and Google Chrome, which isn't a very large segment, all told. Mobile WebKit, however, powers the portable world with the iPhone (and iPod touch) Safari, Google Android Chrome Lite, the Palm Pre/webOS browser, and some Nokia devices. Add BlackBerry to the mix and it pretty much looks like the mobile world vs. IE6 on Windows Phone -- strangely inverse the desktop landscape where IE dominates and Firefox brings up the rear. (FireFox's mobile Fennec browser is still in development).
It was just a couple weeks ago that RIM promised an iPhone-class browser from BlackBerry by next summer, and it looks like this might just give them one heckuva jumpstart in getting there.