Living in MN, we try to take more vacation time in winter than in summer...BUT...I got my scuba diving certificate when we were in Hawaii this past March, and I'd LOVE to get somewhere that has warmer water than up here to do some more diving this summer. We'll see.
PS...I'm not sure where, but I know there is zip lining in Hawaii...you might have to do a little research into which of the islands the activity is on, but I know you will find something :)