Have only had a couple, but last years was the best... upgraded from J to F coming back from JNB to SYD. Was Gold then, but was travelling with my colleague who was WP. Could definitely get used to F.
Also got one from economy to J the week before last from MEL-BNE, but only because the guy in the window seat spilt a full beer all over me, to the extent that I had to get changed!
Another wierd one.... my daughter and I are booked on YASA flights through SYD and on to Albury, and got an upgrade to J for the last leg of the return. Unfortunately had to change the flight and the J upgrade STUCK ON THE RESCHEDULED FLIGHT!?!? Awesome.