Question for CEntrance DACport (http://www.centrance.com/products/dacport/) owners: Have you used your DACport with a laptop while running on battery power only? 
 
As the DACport is entirely powered by the USB connection, how much more quickly does the laptop battery run down?  I imagine it can have a significant impact on battery life.  Any real-world experience out there?

I can answer this WITHOUT owning the unit.  USB can only pass a certain amount of power.  You'd see 3-5% battery life loss, depending on a lot of other things, but you shouldn't see a significant drain.
 
You can test this with any USB device that charges via USB for your own real world test.  Infact, run your media player (with phones plugged in and music playing) and charge something via USB and you'll have an accurate representation of what your battery life playing music will be.

The USB port feeds a maximum of 500 mA at 5V, which means a maximum power consumption of 2.5 W. A typical laptop on battery needs 20-30W to run. Everything is said.

Michael Goodman here from CEntrance. DACport consumes about 350 mA at moderate listening levels, so it is riding well below the USB power limit of 500 mA. This means that it takes even less than 10% of a typical laptop's battery consumption.

Sorry to resurrect an old thread, but I've just got the DACPort in. It does require a stiff amount of juice, but less than the iPad does - a device that won't even properly charge on my laptop. That said, it does run on the iPad with external power. As I keep my laptop plugged in now (iPad is my portable device), I can't give an accurate reading of the battery drain, but I'd assume it is as per above.
 
Currently, it seems well worth the price even though I think a USB-only DAC is somewhat limiting. Low low low noise floor for a USB device, good build and great sound. I would appreciate it more however, if it could run natively from the iPad - reliance on external power is sort of a drain.