We were planning a trip to Bavaria in the summer of 2010, but I see the Oberammergau passion play is in the summer of 2010. Does this mean Bavaria will be espeially crowded in the summer of 2010?
I was in Bavaria in late August, early September of 2000, also a Passion Play year, and I never had problems with crowds. I was in Munich and Salzburg/Berchtesgaden but not in the area around Oberammergau (Fuessen/Garmisch Partenkirchen).
Bavaria is a bit larger than West Virginia. It would have to be a mighty big theatre crowd to overpopulate West Virginia. I think you're OK as long as you aren't looking for a room in the immediate vicinity of Oberammergau.
Here's some number crunching for you. Average attendance at the Passion Play since 1930 has been about 500,000. But of course, this is spread out over a period of about 6 months.
Oktoberfest in Munich, which only lasts 2 weeks, usually draws crowds of up to 1 million people.
So, if Bavaria has enough tourist infrastructure to absorb Oktoberfest crowds, the Passion Play will likely only register as a slight blip. You may have trouble finding lodging in Oberammergau if you don't buy a package deal, but otherwise, it shouldn't be that much different from usual.
Some of the sites, like Ludwig's castles, are always mobbed in the summer, Passion Play or no Passion Play.