Austrian trip next June is a go! We received the invitation yesterday and have already RSVP'd. The happy couple's wedding website is very thorough, with information on travel details (including a reminder that US visitors will need a visa next year), the hotel where they've already reserved a block of rooms, links to the high-speed rail line that will get you from Vienna to Graz, and even what to wear (cocktail dress--an excuse to get a cute new outfit).
We'll certainly stay a few extra days. We both want to see Vienna and N is dying to go to Salzburg for the day.