I think Opera needs desperately a Master password in case of the OS being hijacked.
That can happen if a Laptop is stolen or someone manages somehow to access the computer by overriding the OS password(s).
There are several methods to gain access to a locked Windows-PC. It seems that only an encrypted harddisk (via Bitlocker or such) is safe, but not everybody does that procedure for some reasons.
I understand from the previous posts, that Opera uses the same password as Windows, or the active user account.
With tools like Bart PE one can reset any User account password on a Windows system harddisk, except for those in a network domain (but maybe even some of them, because they have to be stored locally for offline access).
If I understood it right, Opera will follow any changes of the password, so, a thief or someone who can secretly boot the computer with such a tool and then, after resetting the passwords and logging in, can access all Opera passwords.
It's basically a simple "net user" command as an Administrator.
I may sound a bit paranoid, but Laptops are often stolen or even forgotten/lost.
Since there is a growing demand for passwords, accounts and such, if one of my laptops would end in other hands (without my consent), I would have endless work to do, to change those passwords.
On the other hand, not storing them, is not an option (any more). I would need a special app on my phone or on a separate pda to manage them, and I would soon be busy with entering Username and passwords.