Letting your car warm up for more than 30 seconds is just wasteful. Start it up, put your seatbelt on, adjust the radio and go. For the first 20 minutes you're driving, take it easy, don't rev it over 3,000 if you can avoid it - at that point your car is warmed up. Most new cars warm up extremely quickly, but as with any machine, the hardest part of its day is when you first turn it on. There's very little lubrication which is what causes engine wear. Giving the engine some time to circulate the oil and warm it to optimal temperatures does a world of good - but letting the car sit for extended periods of time is just a waste. Today's cars are designed to get up and go after about 30 seconds.