Some articles on tandeming in general are here:
Bottom Line: Riding a tandem is like ballroom dancing. Most folks have the aptitude so, with the proper motivation, some instruction (reading works well in the absence of a tutor), and practice, almost any couple can master the mechanics. The temperment of each couple is the wild card. It has been said and it is true, a tandem will take a relationship where it's headed faster than a New York minute: the strong relationships will thrive and the weak ones will be strained.
Thorn makes a good product that seems to be well adapted for cycling in Europe and 26" tandems are an excellent choice for touring. The US tandem market tends to mimic personal bike buying trends that have been overly biased towards putting the average cyclist on 700c racing bikes thus, that is what you see used most often -- even though easily 1/2 of the tandem teams who own 700c bikes would probably be better served by a 26" model. We're no exception. We still fancy ourselves "go fast" riders and ride a couple of 700c road tandems. If we ever buy another road tandem it would be a 26" S&S model to replace our 700c rigid and 700c S&S models.
As for transporting your tandem, we carrier ours around inside of a Chevrolet Suburban.http://photostore.automark.net/model...r-1500-z71.jpg
. Not exactly practical for most families and certainly not cost efficient given European petrol costs. Short of that, and assuming you'd like to carry your tandem on your 3 Series Beemer, ATOC makes an excellent tandem carrier (Bike Topper - Tandem Model) that is also sold by Thule.
It's features a removable wheel tray extenson for use when you're actually hauling around your tandem but which is otherwise stowed in your trunk. The rack can also be used to tote a personal bike without the extension. There is a more expensive model called the Tandem Topper that features a pivoting head to make loading and unloading easier for heavier tandems (e.g., touring models with racks, etc..) or for anyone who just wants a less physically demanding way to load their tandem to a roof rack.
Finally, as for the coupled tandems, they are great but they aren't for everyone. We have one that we use for trips but it is most definitely a luxury item and not a necessity. As for reliability, they do not degrade a tandem's durability or performance one bit, aside from the added 1.5lbs of frame weight. In fact, they actually make the tandem's frame a bit more stiff which is a good thing. The biggest drawback, aside from acquisition cost, is the need for a moderate degree of mechanical aptitude relative to disassembly, packing, and reassembly. The amount of time and frustration owners have has an equal and opposite relationship with their love of tinkering, organizational skills, and patience.
Hope this is some help...