If you want to try, I downloaded the ATMel Flip program onto a Win7 box, then installed the correct USB drivers by browsing for them in Device Manager.
I then used the SourceForge link to download the Arduino-usbserial-mega.hex file.
I selected the USB device in Flip and then loaded the USBSerial mega hex file and it let me program it with the Run option. At this point I selected the Start Application which switch the Mega 2560 into the USB serial mode rather than DFU mode and the serial drivers appear in the Arduino app on the Mac and I can attempt (and fail) to upload the demokit.pde from the ADK.
However I see other people complaining about a similar avrdude timeout on the Mac, so it could be I have got it "working" as much as I can on the Mac... trying an ADK download on the Win 7 box as I type this, so fingers crossed.