Went last year nice place. I agree with DirtyEddie there isnt much going on and you can walk round the entire city in about 4 hours.
Make sure you go up to the top of the ufo, views are amazing and its not a total rip off for beer when you get to the top, but you do have to pay £6 for the privlidge of going up there.
You can get the train to vienna for about £9 return that is definatly worth a trip.
All in all fun trip who are you flying with, if its sky europe make sure you take a book as we were delayed for 4 hours coming back and this is a common occurance according to the staff.