We have 3 kids - 6, 3, and 1, and will likely add #4 in the nest 2-3 years. We just got a 2008 Mazda 5 on our return from Europe - we are really happy with it. It has minivan doors which is a huge perk, both rows of back seats fold down so that large amounts of stuff can be hauled, and it sits up to 6 - the very back row is really only comfortable for kids for long drives. And it's on a car frame so its not very long and has decent gas. I wish there were more cars out there like this.
Growing up we had a Camry (there were 3 kids) and it was always perfectly comfortable to us, even for long road trips, until my older brother was over 6 feet.
We are moving to Boston though, and so we may sell it. We're trying to figure out how often we'll need a car for out-of-town trips (parents in Northern VT, friends a few hours away, going to the coast, or fruit picking, and so on).
And I love the story of the family biking mother of 6 - it is so inspirational. Obviously not everyone's circumstances allow her exact set-up, but she shows that most of us can probably do more than we are.