Freshly available in Software Update are AirPort Utility 5.6 and AirPort Utility 6.0. AirPort Utility 5.6 is a minor update to its predecessor which "Resolves an issue with using network passwords stored in the Keychain," while AirPort Utility 6.0 is a major overhaul of the user interface that matches its iOS counterpart in both appearance and basic functions. In fact, AirPort Utility 6.0 is so similar to the iOS version that it essentially looks as though its been back-ported.
While AirPort Utility 6.0 certainly looks snazzy and features an interface that novice users will find much easier to navigate, AirPort Utility 5.6 is still around for a reason -- AirPort Utility 6.0 can't be used to administer older, 802.11g-only base stations. People like me who still have an old school 802.11g AirPort Express on their network will have to use the older version of AirPort Utility. This is a confusing and unfortunate oversight on Apple's part, and hopefully this is something the company is able/willing to address later on.
Just from my brief interaction with AirPort Utility 6.0, I can definitely say I'll be reverting to 5.6 for reasons other than hardware incompatibility. The graphically-driven interface feels nice and natural on iOS devices, but it feels far too dumbed-down on the Mac. Critically, in AirPort Utility 6.0 the entire program is unusable if you happen to be updating firmware on any one base station; administering any other base station is impossible if you're updating firmware on any AirPort device on your network.
For novice users with supported AirPort devices, AirPort Utility 6.0 will be a much easier way to administrate their wireless networks. The rest of us may prefer to stick with the old interface; I know I will.