Matt,
I was in Queenstown the first week of May. I have been there in the middle of winter before for skiing and it is chockers full of people. It is quite exciting. Make sure you go to Fergburger. *drool*
I didn't get to do any activities apart from walking and photographing. I lost a few days due to rain on my trip from the east to the west coast. I wanted to jump out of a plane, and go on a jetboat, but, I was just pressed for time.
I did do a scenic flight around Mount Cook from Lake Tekapo. It was splendid.
Regards,
Humayun