Have you noticed your hybrid(Toyota) making unusual sounds after it is parked. Guess what! The Toyota Hybrid system has a thermos storage system that pumps hot antifreeze into an insulated (Thermos style) storage tank that keeps the fluid hot for up to 8 hours. When you restart your Hybrid, say maybe 2 hours later the pump pumps the hot antifreeze back into the radiator so you have almost instant warm up of the gas engine. I guess a block heater would help for an overnight park but short (under 4 hours) of parking probably wouldn't need a heater. B)
Luke
The Prius is about 50-50 city highway, most of the time with a car pool person.
By the way, for Cold weather driving? Get yourself an Electric Block Heater (EBH), you'll never regret it. The EBH install isn't so complicated that you can't do it yourself, with limited tools & mechanicle skills. If you have decent skills you can knock it out in less than 2 hours. They'll REALLY boost your mpg's in the winter, especially on short trips, like when your average trips are under 10-15 minutes. Plus, the EBH will let your cabin heater come on extra quick as an added benefit. Nice on those sub ZERO days!! They're only $70 or so from Toyota (interchangeable with the Hy-Hi SUV) Dealer, and on line maybe a little less. Put it on a timer for maybe 90 minutes before your trip starts & you're good to go.
Enjoy