I take the caltrain & shuttle quite frequently, if the line of cars waiting to drop passengers off is long(like at certain times this past thanksgiving) it can actually work out to take about the same or less time to do that (and significantly less money of course). The shuttle is no speed demon of course and you get to have the joy of passing through the long term lot on the way to the terminal.

The elite line is usually short, and the elite security shortcut worked great for me last Monday morning when I was cutting it a little close with about 30 minutes left till flight departure when I arrived, luckily I had already checked-in online and with the security shortcut was able to get to my gate just as they started boarding.

Make sure you check train and shuttle times online to make sure your schedule is ok, the train is usually on-time but it's always good to be safe and get there a little earlier. Aiming for a 1-hour prior arrival should be fine.