Don't have one, but I've toyed with the idea of getting one (or two) for a couple of years. If I only had two kids I think we'd have plunked for a pair so that we could go bike camping again. That third kid really cramps my style.
Anyhow, I rode a metric century yesterday and I saw a Dad with his daughter on a beautiful red Cannondale tandem (road bike style) and another couple on a old steel one (didn't get the brand). The Mrs and I tried one out back in the 90's. Being a controll freak she loathed it - which is too bad because I thought that paired with a trailer it would be a great way to tour and camp.