Just a quick notice: I installed Opera mini today on my Lumia 920 and as opposed to other users, in my case the app doesn't start at all (it just hangs on the loading screen: http://bit.ly/1CQDQnl ).
Some quick info about my phone:
Phone Model: Nokia Lumia 920
Firmware: Lumia Cyan
OS: Windows 8.1 Update (Build ID: 3051.50009.1424.10362)
Other info: running Developer preview