We've always enjoyed trips to Vienna and other parts of Austria, and found the people to be very friendly (especially compared to Germany, where we've lived and still have many friends). Some things we've enjoyed doing, which may or may not appear on a traditional tourist itinerary are the following:

Rent bicycles, pack a picnic, and take a half-day bike trip along the island in the Danube. We rented from this place, which is run by an American ex-pat: http://www.pedalpower.at/

It may sound dopey, but take a Johann Strauss dinner cruise. Food was predictably mediocre, but the people singing were quite good, and overall it was really fun: http://www.ddsg-blue-danube.at/ddsg_ewien.htm

Take the streetcar one evening to one of the wine areas in the suburbs (Heuriger), walk around, and visit some of the wine-bars.

Besides Vienna, I think Melk is worth a half day to visit the monastery. In the Czech Republic, consider a trip to one of the old spa towns, Marienbad (Marianske Lazne) or Carlsbad (Karlovy Vary).

Carol in rainy Boulder