Maybe I don't count, because part of my motivation for bike commuting is environmental. So if I drive, I get guilt, which ruins it anyway.

Actually, this is not even applicable for me since last December, when I gave up my personal car. Now I don't really have a choice. If I drive the family car, the rest of my family won't have it for the day. Or I inconvenience them making them drop me off and pick me up. Either way, it's easier just to ride. (I should state that it's only 5 miles each way.) And since giving up the car, I've discovered an even deeper joy of feeling that I don't really need it anyway.

Look at it this way. Do most people enjoy driving their car to work? No, they just have to get to work somehow. So, don't feel bad if you aren't always filled with glee at the thought of getting on the steed for another day of battle. Would you really enjoy driving your car more? Well, okay, if you do that sometimes, and it keeps you from getting burned out bike commuting, so be it. It's your life. Maybe if you give yourself some car days, you'll start missing the bike ride and be more motivated to take it up again. Marriages don't end just because the honeymoon does.