Very pleased with Remote running on my iPhone 3G, can control different libraries (i.e. on different machines), and provides for multiplay control, can also control AppleTV -- you must choose whether it should control an ATV or a stand-alone Mac.
Same GUI as Signal and Remote Buddy, instant response, both to the touch-command and from the Mac mini - with tracks changing immediately, and with pause/play also responding immediately. Similarly, coverart is ported to the device very fast, faster than both Signal and RB.
Very pleased that Apple has now finally provided an app, and that it's free. It does not control peripherals, but I can see from the appstore that several remote solutions are up, including one called Control, if I remember correctly, which requires installation of the hardware control units.