Ditto, I keep mine hooked up to my iMac via the optical out of the Mac. Use it as a DAC for a T-amp based computer playback system, and also use it as a headphone amp -- makes for a good desktop playback system.
Since I change my gear around every 5 mintues, I sometimes think about getting rid of the USBPre for some other taping gear. Though it is also great taping gear, I often end up keeping it around for it's dual use in my playback system.
Too bad the USBPre 2 jumped from $650 to $850, makes it a harder sell for hobbyist tapers. Still, it has very nice preamps, excellent A/D, offers lots in the way of options and inputs/outputs, and doubles as a good piece of a playback system. Pretty versatile piece of kit.