I don't have experience with it, but have looked at it since we will be in Salzburg this summer, also. If you have the Rick Steves Germany book with info on Salzburg, he mentions the card in his section "Tourist Information" and says it could be a good deal if you intend to visit several of the places offered. He has negotiated discounts for many places, also. So for example, his discount on the Mozart Dinner Concert is 9 euros on a 59 euro ticket.
On the www.salzburg.info website, if you click on "hotels/offers", then on the Salzburg card, information comes up. One of the picture/links says 'Free with card" and one says "Discounts." When you click on an offer, such as the Mozart Dinner Concert, you can click on price. It shows a 10% discount and something about 'advance.' The Panorama Bus Tour has a 20% discount. You can check the discounts for other things against what Rick offers.
First, I will figure out what we want to see, and see if the card matches up with that. I haven't sat down to figure it out yet myself, but will have to include the cost of the card in my calculations.
Maybe someone else with experience will chime in here.