Ifkip I've heard about that Irish having to refuse tea three times thing before and I've often wondered... what if you don't actually like tea? Is there an accepted way of telling your host that so you don't keep getting asked?
I've spent quite a lot of time in Austria, and apart from the popularity of slippers that has been mentioned already, the things that struck me most were:
You don't get invited to people's houses (or more often flats) unless you've known each other well for a long time. They're more likely to suggest meeting up in a café. This doesn't mean they don't like you, it's just their way.
If they even suspect that you might be an English speaker they will often insist on speaking English to you, even if you answer in quite good German.
Tea and coffee are not automatically served white (I don't like them white anyway, but if you do, it's worth knowing). White coffee is called brown coffee (einen Braunen).
Sweet dishes are sometimes eaten as a main course, especially at lunchtime.
A lot of snow is really not a big deal.
Not much is open on Sundays, except in very touristy areas.
"Palatschinken" is nothing to do with ham (Schinken) - it's pancakes. So you don't need to throw up your hands in horror if someone offers you some with ice cream and chocolate sauce!
People used their titles and qualifications all the time. You might see an advert that says "room to let in flat-share, contact Engineer So-and-So" or receive a wedding invitation saying that Heidi X is marrying Holger Y, MA.