While GPS receivers are supposed to use 23:59:60 a receiver I was testing the last time there was a leap second did indeed generate 23:59:59 twice. Our software now accepts either. We're getting started on a new system this year, hopefully we'll get a selection of GPS receivers wired up to see what they do on June 30th.
Hybrids do make use of the battery and motor during highway use. When going downhill the engine will shut down and the battery will charge. This charge will be used by the motor on the next uphill to reduce engine use.
For plug-in hybrids with their large batteries several miles of all electric range can be generated on a long downhill.
Ford did an update to the MyFord Touch infotainment system last year this way. Downloaded a bunch of files onto a USB drive, plug into car, wait 20 minutes. Since it uses an automotive version of Windows CE of course it needed to reboot a half a dozen times during the update. But for power-train related updates you have to take it into the dealer.
I bought a Ford C-Max Energi plug-in hybrid a couple of weeks ago. It's positioned between the Prius and the Volt in the marketplace. My usual trips around town fit nicely into it's electric-only range while having the gas engine for trips out of town.