I only ride to work half the time (the other half of the week I telecommute). By the time my "ride to work" block comes around I'm usually excited to get back on the bike.

That and my only real alternative involves having my wife + 3 small children all pile into the minivan to drop me off and pick me up (we've only got the one car). That'd be another 40 miles / 2 gallons of gas plus the logistical hassle of it all. Better to just ride.