I've had a Garmin Streetpilot III GPS since about 2003. I keep it on my motorcycle most of the time, although sometimes I bring it along in one of the cages. It's getting a bit old, and I dropped it the other day which kinda screwed up part of the display, but it still does (most of) what I need.
For all of that time, though, I've powered it through a bit of a Rube Goldberg contraption. The auxiliary power socket on the bike powers a BMW -> Cigarette Lighter adapter. This adapter then receives the power/speaker cord from the Garmin, which rests in my tank bag. Another wire comes out of the tank bag to hook up to the GPS unit's power and sound ports. It's a bit of a wiry mess, and sort of inconvenient when looking through the bag for stuff.
Well, I've had quite enough of that. The other day I hooked up with pfranc.com (purple computing) and hooked myself up with a couple of ready-to-assemble power plugs. I plan to tear into the motorcycle's electrics and hook this up properly one day Real Soon Now. Since I need fused power, I may just go ahead and run it off the same circuit it uses now.