I think the 'ride part way with the wife, then ride home with the wife' plan is an ideal way to start. (Also give you an excuse to buy an nice bike rack, if you don't already have one ) That way you can ramp up the distance a little at a time, and make your daily ride as long or short as you want it to be (and if you're like many bike commuters, you'll soon find yourself wanting it to be longer ... and longer...).

My commute, these days, ranges anywhere from the bare-minimum 4.5 miles to 15 or more, depending on whether I have time to play around on the bike (I often leave early in the morning so I can do 8.7 miles instead of 4.5). I like the idea of the '40 mile shortcut' someone mentioned above!