All of the ED details can be found on BMW's website.
BMW transports the car just as they would if it was new. You just drop it off with the boat when you're done.
The difference is, you start paying for the car when you pick it up. BMW will cover the payment while it's in transit (at least on a lease, not on a purchase I don't believe) but that means you'll pick the car up, drive it around Europe, then have to wait while it is being shipped.
The downside of course is that you'll drive the car, be completely in love, and then have to live without it for a week.
Also the other obvious point is while you'll save some money over the standard MSRP (It's not 7% across the board, visit BMW.com or bmwconfig to see the ED difference for each model). You'll spend most of that money or more on the airfare, lodging and travel expenses for you (and possibly a friend or significant other). But it's a once in a lifetime gig so it's definitely worth it if you can swing it.
Also don't forget that most of Europe can have nasty winters, so it only really makes sense to do it when the weather is still nice. No one wants to get their new car only to be stuck in a German blizzard.
Current: '15 M235i Vert
Previous: '13 335i, '08 TL-S, '00 Corvette