Not an aviation nerd, but had a local one explain a particular A380 issue to me. About once a month the main daily SYD/MEL to LAX routes had to turn around and it was pretty much always the Rolls Royce engine (one of two engine manufacturers for redundancy). And then it started happening on the other engine as well. Can't confirm the frequency, but when I was talking to a Qantas crew member about this over a year ago he nodded and said they won't be purchasing any new A380s. He said he felt they were bought for the marketing "me too" reason more than anything else.

EDIT: That being said I loved the A380, I frequently flew premium economy intl. on it and even if you could wrangle the small (something like 20 row?) economy section upstairs it felt less like cattle class.