QL-I don't think that Prague has converted to the Euro yet. They joined the European Union in 2004 but are still using the Czech Koruna. As long as you stay away from the high priced areas in Old Town Square, Prague is cheap. Before going make sure to get a Rick Steves Eastern Europe guidebook. It has good information about restaurants, tourist sites, etc.
You are correct Money. I was assuming that they would automatically use the Euro when joining the European Union.