A collegue of mine has a turbo'd MX5 and he's running a Greddy e-Manage Blue fuel management system. It was all set up and running and he drove to work on the morning. He downloaded a new map for it and decided to reflash it at lunchtime from his laptop.
The laptop has a really, really crappy battery... It died while doing the reflash, and the car wouldn't start due to the corrupt map it was now trying to use. He had to push the car through the car park (he's on a huge site) to underneath the window of the office where he works, dangle the power cable for the laptop out of the window, connect it up and flash the Greddy box again.
I'm not making this up...