The guys at SoundMan Car Audio got an early start installing what they called the "first ever iPad in a car" sound system, starting a couple of days after the iPad became available. As we highlighted here when they released the video of the beginning of the install, they had opened the dash of a Toyota Tacoma pickup to create a built-in iPad car audio system. They've just posted video of the second phase of their project, and apparently they ran into some trouble trying to get the iPad to interface with their sound equipment. Nevertheless, they deserve kudos for being out there early on, dedicating serious man-hours and some pretty expensive hardware to learn the capabilities of the device. They've since moved onto a second project, which is a car cradle that allows users to take their iPads with them when they leave the car.
SoundMan designer Doug Bernards had laid out an pretty trick design, planning to plug a cable from the iPad's dock connector into a Onkyo ND-S1 which would transmit the digital signal from the iPad directly into an Audison Bit One, which would act as a D/A converter and process the audio signal. They had build the Bit One's controller into the Tacoma's dash for adjusting the volume and audio settings. Unfortunately, they couldn't get the iPad to talk to the Onkyo, so they ended up just using the analog audio out from the iPad, and added an iPhone dock for their digital source.
They weren't content with just one iPad project, however, and so started a second project with a Nissan Maxima. Most users wouldn't be interested in dedicating an iPad solely for car audio use, so they worked out an ingenious cradle for the iPad to rest in. They connected the iPad via the analog headphone jack to the aux in of a double-DIN Kenwood eXcelon receiver. When the iPad is removed from the dash, there's a smaller display that shows the video from the Maxima's rear facing camera.
Video of the Maxima install is below.