I didn't actually stay in, or visit Qui Nhon, but did stay two nights in a hostel on the beach nearby. It was called Life's a Beach and it was the best hostel I stayed in all trip. It had a private beach and a bar that served brilliant food with amazing views over the bay. Although it was originally going to be a stopover from Nha Trang to Hoi An, I stayed an extra night because it was so relaxing as opposed to the frantic days of driving and sightseeing that came before.
There are some hidden waterfalls nearby that you can walk to, but I preferred to just relax myself.
Two nights of full food, quite a lot of drink, and accomodation, only came to ~$35. If I ever return to Vietnam I'll be dropping in here.