Absolutely worth doing even in milder climates. My Escort and Tercel don't even get up to full operating temperature at this time of year for the work commute. A block heater in the Tercel however makes the morning trip downright toasty. I'm close to putting the Escort back into insurance suspense and driving the Tercel again for the winter for this very reason.
A space heater inside is a nice help too on frosty mornings, but I absolutely would NOT do that part without a timer that switches on AFTER you awaken. I setup mine at 750W coupled with the 1kW block heater to come on 45 minutes before I leave.