This is kind of silly, but I recently got it in my head that I wanted the ability to capture a time lapse of a roadtrip. The problem: most of my trips are too long to cram onto a single DV tape and most camera batteries wouldn't last that long, anyways.
The solution: install an inverter, mount a laptop in the trunk, use a firewire connection to a DVcam mounted with velcro on the back trunk privacy cover, and use gawker to snap a frame at a certain interval.
(hint: the camera is hidden under the hat. It isn't really noticeable unless you're looking from the front of the vehicle and know what you're searching for. Only the round lens is barely visible.)
It takes a bit of planning to get a comfortable frame and capture rate, but the results can always be tweaked in a video editor. This setup works with the vehicle off and will remain powered throughout the night if you decide to stop somewhere and want to keep the camera going. You could drive from coast to coast and compress the entire trip into a fifteen minute video if you wanted to.
Results of a three hour test run from Port Charlotte to Weston, Florida, can be seen, here. (quicktime .MOV ~19.3Mb)
My next test will be Tampa to Atlanta, a trip with a duration of about seven hours.