Plug in??
Its only gotten down to 17 so far this year, and my '03 truck started fine with just one 'glow'. I am hopeing that Santa will be good to me and bring me an Espar heater for my truck before Christmas.

before the 'real' cold weather gets here.
I work a 4PM to 4AM shift, and last year I was driving a gasser S-10 4x4 with the 4. 3L v6. It had a remote starter installed and it was nice to get out to the truck after my shift and have it be warm when you climb in to it and most of the windows clean. I would like to be able to do this with my new truck.
The thing with plugging in seems to be that most of the time you really want to have it, you are out away from any outlets. I have no access to outlets when I park at work.
Since this is my first winter with the Cummins engine, I can't say much about how it starts when cold, but I think at the next oil change I am going to switch to a 5w-40 Synth. RotT. It should flow a lot better when starting than the 15w-40 stuff that is in there now.
I have used 5w-30 and 5w-40 synthetics in my cars, and they start up just fine with just glow plugs down to about -15. Below that I don't go out much!
At low temps, starter motor RPM is a big factor in how well a diesel will start, and cold thick oil don't help the cranking speed.
My '87 MB 300SDL has an electric coolent heater in it and so does my VW TDI. While the TDI is direct injection like the cummins and starts easy when cold, the MB is indirect injection and it grumbles a bit about starting when cold, but it still starts OK when -0 outside.
With the TDI when its cold out, it burns so little fuel (50+ MPG's!) that the engine does not make enough heat to bring up the engine temps to operating temps until after about 10 miles at 65 MPH. I feel this is not good for the engine, so I plug it in if I am planning on going only a short distance when it is cold out. It still starts OK without being plugged in, but I think it is better for the engine. It keeps the oil from collecting moisture, and the engine runs more effeciently when warm, and I get to stay warm too!
Just my $. 02 on it. .
Arnie