Prague on a Sunday?

I was just in Prague and early Sunday morning is a great time to see the Castle; you can beat the crowds. But, you cant go in St Vitus Cath. until after 12 because of regular church services.

In Europe in general (very general), the day sights are most often closed is Monday, not Sunday. Sunday, on the other hand, has many more store closings than we are used to in the US. So, unless you're shopping, or you have your heart set on something specific, you'll do fine in Prague on a Sunday. Of course, you do have to check for specifics on each place, but you won't be without things to do. Note that the Jewish sights are closed on Saturday, so they get more crowded on Sunday, but they are open.

Yes, my wife and I were there last May. We actually attended the early mass at St. Vitus on the Sunday we were there (I think it was maybe 8:30 or 9:00 a.m.). There were gentlemen outside keeping tourists out, but when we said "mass," they let us in. You obviously have to be respectful of the services and sit quietly during the mass, but you can actually get about 15-20 minutes to wander inside at the conclusion of the mass with almost no tourists there. Plus, although I am not Catholic, it was nice to experience the services in Czech, and to see the subtle differences between an American mass.

The rest of the castle complex was also open. Don't miss the Lobkowicz Palace - it was one of our favorite things we did there.

Also, we ate lunch at the Klasterni Pivovar Strahov, near the monastery, on top of Castle Hill. The food was excellent, they brew their own beer, and it was cheap. It's in Rick's book. Just don't go to the touristy restaurant that is right next door - make sure you hit the brewery part.

Prague on a Sunday is a great idea! Most things will be opened, including the Prague Castle. So no worries.
(I wouldn't be so sure about Bavaria, though..)