Same here. On Windows 7 x64, with Opera 24:

• Main window is always on top of other applications (in full-screen and also in windowed mode)
• In full-screen, I can't access my Windows auto-hidden taskbar.

And just as said Mesecur before me, it prevents me too from working efficiently, and I would add that it's a very big annoyance. I was defenitely happier back when Presto was still here...