My husband and I got married at the Mirabell Palace in Salzburg in April 2010, and spent a week in the city.
It is a beautiful city with Salzach river winding through the middle separating the old and new town areas. The Mirabell Gardens are beautiful and were a wonderful location for our wedding with the fortress as a backdrop.
The Old Town is where the majority of the sights, shops and restaurants are, but the New Town also has shops and restaurants. The Old Town area is easily accessed over the Makartsbridge (footbridge) only 5 minutes from the Mirabell Gardens.
The fortress is worth a look, we walked up to it; its a steep climb but not far, and worth it to take in the views on the way. Salzburg has a lot of large squares, cultural and architectural sights. Try getting off the beaten track and exploring, walk up past the Museum der Moderne and on to the castle, or up into the hills on the other side of the river for spectacular views.
We also did the Sound of Music tour (of course) which takes you to the main locations in the film, but is very cheesy with the soundtrack playing on the coach during the whole tour. We did the Bavarian Alps and Saltmines tour as well which I would highly recommend. There are a couple of booths near the Mirabell palace where you can book trips, or your hotel will usually book them too - we used Panarama tours for both our trips (discounts if you book 2 together). Buses are frequent and €2 for any one journey. Take a bus to the Helbrunn Palace to see the Trick Fountains (quite impressive) then walk through the gardens of Helbrunn up to the zoo - great for old and young alike.
During our stay we had very heavy rain showers followed by bright sunshine, our wedding day was warm and sunny, but the day after was very heavy rain - it changed very quickly every few hours! Overall Salzburg is a very pretty, romantic city with lots to do for all ages - our wedding party of 24 people ranged from 10 - 85 years old, and all thoroughly enjoyed their time in this beautiful city.