You shouldn't pay more than $1k over invoice (not MSRP). ED is pretty much a no-brainer for many dealerships. Your car does not come out of their inventory, so it's just gravy for doing a little paperwork and hadning you the keys.
We did our's toward the end of '06. Flew 2 for 1 on Lufthansa to Munich. ! night in Munich (Marriott), pick the car up the next morning, drive to Florence, Italy. 3 nights in Florence, drive the Grossglockner, two nights in Austria, visited the Disney Castle (easier to spell than Newschwanstein???), another 2 nights in Munich (Marriot again), dropped the car off at Harms, took the shuttle to the airport.
Very, very easy. And an amazing trip. You'll come back with a whole new appreciation for driving (if you get onto the Autobahn and Autostrada) and disdain for dub-ass U.S. drivers.
I think we came back with $400 more in our pockets than if we bought the car straight from the dealership's floor.
We just bought an '08 M3. WE would have done another ED, but there's no discount built into the ED program for M's.
There are only two downsides I can think of.
1) You are paying for the whole trip. The money you save over MSRP (or non ED-selling price) isn't financed like the car payment. So, you have to have that cash available.
2) It'll take 7-8 weeks to get your car back once you drop it off at Harms (or it gets back to them if you drop it off at any of the other approved locations).
Kind of tough to trade a car in this way.
Warning - You'll want to set up WAY more stuff to do and places to go than you really should. Narrow it down. Even still, you'll be dead-ass tired when you get done.
And, read all the posts where andytaro suggested.
Don't fear getting around Munich via public transportation. It's wicked easy, even for a Hic like myself!