I'm going with
@James_Dean on this debate. It does depend on where you are flying and what you are flying. If you have a capable most weather (no such thing as all weather) airplane you can beat the airlines door to door for much of your flying in the country with a high dispatch rate.
Yes, there are a lot of variables. If you live in the suburbs of a big city like myself, it takes 10 min door to hangar vs 45 min door to parking garage at the major airport. When you get to the hangar you have your plane that is how you left it last making the pre-flight and go very streamlined (weather briefs and flight planning have been streamlined by technology). When you get to the major airport you have to find parking, make your way to the terminal, get in line, check baggage, get in line, go through TSA (the bonus here is stripping down and getting felt up), and get to the gate early enough to ensure all the line up and waits don't make you miss the flight. Private plane gets you to the small airport exactly (or very close) to where you want to end up. Airlines, many times with the hub and spoke system, get you to another major airport, deplane, make your way to the other gate and wait because you can't schedule too tight of a connection for risk of missing it. Then you make it to a larger airport that many times requires you to drive 45 min or more to where you wanted to end up.
Long story summarized, if you have a capable twin or well equipped single, you can and many times will beat the airlines which saves you time in your life. As James said, many times you actually save day's off of travel. You don't have to deal with TSA, airport parking, airline schedules, etc. I feel more refreshed flying myself when I get to my destination than I do after the hassle of airline travel.
Of course this is all just one guys .02 cents.