How often do you have more than 2 ppl in your car?

I am in the early stages of new car shopping (to replace my 94 Audi Cab w/ 170k miles) and pretty much narrowed it down to a pre-owned (still debating e36/e46) 3xx convertible or a preowned boxster. The one thing that really makes me think twice about a boxster is the inflexibility of two seats. I need to get a better grasp of whether I'm making this out to be more of an issue than it really is. Right now, my wife and I have no kids (probably stay that way for 3 more yrs or so), and rarely do we actually drive around with someone in the back seat, but still I like having the option of taking the convertible on a nice day and shoving someone behind us.

Figuring everyone here has very different lifestyles, how often do you use your backseat to carry a passenger?